Any

this has been discusses many times, and there doesn't seem to be a good enough reason/approach to do that.
essentially, multiple severities per trigger requires writing two expressions. essentially you end up with two trigger editing forms on a single page, but you lose some flexibility because you can't set comment or dependencies individually.

while trigger editing could be improved in many ways, tucking multiple severities in a single trigger currently does not seem to add any reasonable functionality, except being more familiar to those who are used to other monitoring solutions

You don't need to go with two trigger editing forms on a single page. It does add reasonable functionality. One good use case is to have the severity of a free space trigger change depending on how much free space is left. It would certainly save a lot of effort and a lot of clogging up things like the overview page when monitoring a heap of partitions for free space. Currently you would have to multiply the number of partitions by the number of severity warnings to show the number of triggers. ugh

My suggestion is to add a comma separated list of values at the end of a trigger. For instance -

Expression:

<10,5,2,1
Severity: Warning

Which would mean that when the root partition is less than 10% free, the severity is the one chosen for that trigger (Warning); when less than 5% free, the next severity up is chosen (Average), etc.

If people want to set comments or dependencies individually, then they can use separate triggers as they do now.

No loss of flexibility, and makes certain common tasks simple.

I'm all open for alternatives.
I do think this would bring an unvaluable enhancement to the way Triggers are currently defined.

Currently besides having multiple almost equal Triggers for different thresholds,
we have to manually guarantee there are no overlapping values in the Triggers condition.

Take these different Triggers,
Warning: > 80% & < 90.01%
Average: > 90.00% & < 97.01%
High: > 97.00%

Wouldn't it just make more sense if there was an option available to group it in a sole Trigger instead of spanning it through three?
It's not just because some users are used to this,
it just makes sense.

Should be revaluated for Zabbix 2.0
Both individual comments and dependencies to each Trigger don't bring as much gain as a unified Trigger would for complex situations with multiple Thresholds windows.
Plus, the active Triggers window would become much more cleaner

there still doesn't seem to be a valid approach. overloading trigger expressions would make it nearly impossible to work with them - what about an expression like

&

, how would one stuff multiple severity references in that ?

currently it seems that a better approach would be to improve working with dependencies and maybe the trigger creation process

I would say that this idea could be implemented in a different way: have separate triggers, have a chance to combine them to a single box in an "overview". The idea is to save some space on this screen. When you have lots of hosts and lots of triggers you do your best to get them all on one screen, and having 3+ similar triggers isn't a good approach.