Beside just having the mentioned functionality in general it might help in connection with auto-registration too.
We use auto-registration for automating some tasks like adding hosts, setup interface, setting right proxy, linking templates, assigning host groups, etc.
This works really nice and saves a lot of manual work.

But if we want to "reserve" host names for future use it's not working that well.
When adding hosts for reservation we often don't know yet their ip addresses nor do we want to do tasks covered by auto-registration manually. Thus we just create such hosts by defining their host names only (and leaving the pre-defined Agent interface as it is).

Now when the hosts get discovered/registered they get an additional (2nd) Agent host interface with the real ip/dns/port. But due to the fact that it's an additional interface all items will be assigned to the first Agent interface (127.0.0.1).

• by the way alias per host interface like mentioned in ZBXNEXT-735 might here be useful too

Finally we have to edit every host copy&paste ip+dns from 2nd interface to the 1st one and remove the needles second one.

ZBXNEXT-1925 could allow to set initially a dummy host interface which may but don't necessarily have to be removed after discovery/registration
No manual intervention would be needed to operate properly.

this might be complicated. i assume the dummy interface could have items of all types assigned to it, thus creating a new "normal" interface would only move items of that type over.

• ZBXNEXT-2156 asks for an ability to create hosts without interfaces
• ZBXNEXT-3443 asks for a "generic" interface

this might be complicated.
most likely, yes

i assume the dummy interface could have items of all types assigned to it,thus creating a new "normal" interface would only move items of that type over.
Exactly. Iirc, then the dummy interface was supposed to be something available in a host implicitly. When creating or linking items a host has no regular interface for, then the dummy interface is automatically used - as a placeholder. It's not supposed to be something a user may select.
This would remove the constraint of having proper host interfaces configured in order to link or create items. Same applies to removing host interfaces where still items exists for.

Now host interfaces are optional for items that do not require it. I believe this ticket can be closed.

Well, removing ZBX interface goes only half way, because it leaves IP/DNS column in hosts table empty.

This makes it harder to understand what host is broken both in Hosts and in Trigger Action notifications.

A generic interface, would still be nice way to set this IP/DNS column for inventory purposes.

Looks like ZBXNEXT-4660 is only generic interface ticket left open.