For me this is a showstopper. Maintaining takes many times longer without these.

Functionality to add multiple hosts to host group (also applies to templates) is still present in form of mass update of hosts (in scope of ZBXNEXT-4725 it was made more useful for such operations). From my point of view it is even easier, than adding hosts in host group edit page.
1. In host list you can filter out only hosts, you are interested in, select them and via mass update add new host group for them. There is no more need to search for each single host in big list, where at each time you see only small part of it.
1.1. In worst case scenario (if you can't filter out the subset you need), you will need to go through same amount of hosts, but this time via host list, where it should be easier to navigate, than in small list, as it was previously.
2. By mass update you can add several host groups to hosts you have selected. (no need to search for them in each host group you are adding them to)

Also I should add that having such list of all hosts in Host group page on huge installation will introduce performance issues (it was one, if not the main, reason why this selection was removed from there in first place).

You are saying, maintaining hosts and/or templates takes longer. But I don't see, why is should be so, if you are using mass update. Can you, please, explain your use cases?

Yes, you can add new template to hosts with mass update, but you can't remove hosts from template with mass update. This used to be trivial, click, scroll down, shift-click and click > arrow.

It is possible to remove one or multiple host groups from selected hosts via mass update.
It can be done by selecting "Remove" radio button in mass update edit form. It will remove only selected host groups from selected hosts.

Olli, I just hope you know that by that "removal" sequence you just unlinked the template from the host, leaving the actual items "orphaned" on the host level. It was a cool feature if you know it but at the same time could leave a huge mess on the host level. 

Valdi, Mass update can't nicely unlink (and clear) a single template. And one more use case - you could create a new template and immediately add it (yet empty with no items) to selected hosts. Now you have to go through all the mass update hassle to do it. 

Additionally you can't even see what hosts are linked to a template from Configuration -> Templates -> Opened template view. 

Valdi, thank you for mentioning this functionality - it is indeed working as expected.
A big usability problem is that Zabbix frontend has become even more fragmented than it was before. That is, one cannot find or easily reach the desired functionality from common source locations.

For example, a very simple and fairly common scenario:

1. Take a look at some host.
2. Switch to the template tab.
3. Notice a template of interest, and have a need to check what other hosts are linked to it.
4. Click on the template name.
5. a) Older versions of Zabbix: see the information you need.
5. b) New versions of Zabbix: no way to get to the information you need.

The usual workaround would be to copy the template name, go to Configuration -> Templates, expand the filter, paste the template name, click Filter.
Oops, that only gives up to 50 entities by default, and they are crammed in a single table cell, and not even an entry per line.
So as a workaround that is pretty lousy.

The usability regression there is also mind-boggling. Every extra click is a big burden for repeat operations, and here we have not only many extra clicks, but also the need to memorise this sequence - infrequent Zabbix users will give up instead (empirically tested).
The access usability regression could be fixed very easily - by providing a few links from the host/template properties (to go to a filtered host/template list). I might be missing something very obvious, but it is unclear what holds back ZBXNEXT-5020.

Of course, fixing the interlinking would not help with the template downstream entity listing being pretty much unusable beyond a dozen of entries.

Update:
Please note that the reason for the removal of that exact feature is clear - in large installations that functionality not only was not working well, it was also a big performance problem.
While it is possible that extensive brainstorming happened in secret and excluded all possible solutions, it seems a bit far fetched.

Ingus, I was not aware of that. That is/was crazy bad design! However, problem persists: there is no easy way to unlink "and clear" template from chosen subset of hosts.

I think that template added to host ++group does not reflect to hosts under same host group, right? I tried it with 4.2.3:

1. Created new template
2. Added new item to template created on step 1
3. Added template created on step 1 to existing host group

Item added on step 2 did not appear on host in host group used on step 3

So workaround/workflow Valdis suggested does not work.

Sorry olli, I misread your second to last message, now I see it:
In mass update, you can remove all templates from hosts. If you are updating many hosts with same templates, you can replace templates with same ones, except the one, you want to remove.
But yes, you can't remove single template from hosts with different templates.

As for ingus.vilnis comment, there is an option to clear the hosts, when mass removing templates: Clear when unlinking. Or you was meaning something else?

I see the usability issue you are mentioning, richlv. I am not really in place to comment it, but I can say: "Thank you for explaining it".

It is kind of in the comments, but I will write it more explicitly:

• To see, what hosts are linked to template, you can go to host list and filter hosts by template.
• To see, what templates are linked to template, you can go to template list and filter templates by "Linked templates".

But, as richlv mentioned, there is a usability issue here, as it requires more steps to do, as you would normally want to.

The workaround I suggested was to add/remove host groups from hosts/templates. The problem with templates I explained in my previous comment.

You are right olli, the templates, added to same host group as hosts, will not be linked to these hosts. Sorry, my message confused you.

Yes, I know that you replace templates. However, that is not sufficient.

For example, you have:

1. mail.example.com
   1. Template tape backup
   2. Template IMAP
   3. Template SMTP
2. web.example.com
   1. Template tape backup
   2. Template HTTP
   3. Template HTTPS
3. web1.example.com
   1. Template tape backup
   2. Template HTTP
   3. Template HTTPS

And so on, tens, hundreds, thousands of hosts, and you need unlink and clear "Template tape backup" from these hosts. Can't replace since they have different templates.

Richlv i'd say not even a link to a filtered version, just add filter there and then, perhaps default to whatever seems sane.

please bring this functionality back.   here is how I often use this.  I have a group that is called "Paging"     if I edit this hostgroup, I can see which hosts which are not in the hostgroup using the selectors.  By selecting different hostgroups that I know should have hosts in the hostgroup, also to be able to remove them.     Now I have no idea how to accomplish this.      I use this mostly with hostgroups and not with templates because of the issues about unlinking. 

Many of us manage ad-hoc maintenance windows with a group called "Maintenance" and require the ability to manage a hostgroup (not a host).  Having a UI that allows us to manage the group it crucial. 

Here's a good use case: I get notified of a short notice outage in a remote site.  I have over 100 hosts groups there.  Before 4.0, I could add all of these hosts quickly to a Maintenance group.  Now that operation is:
1. Configure -> hosts
2. Click Reset
3. Configure a filter to display the hosts you want add to a hostgroup
4. Select all hosts
5. Click Mass Update
6. Click HostGroup
7. Click Select
8 Select group(s) from the list
9 Click Update

This workflow is also much more difficult to explain than the old hostgroup two window UI. 

Since our upgrade to 4.4 Zabbix has become less useful because we can't quickly disable alerts and escalations.