Of course you can !
I'd give you the example of the Cool Collar, just to speak about things I scripted myself. But there are other AOs using the new animation overriding LSL functions and that are fully customizable.
It's up to OpenSim developers to implement it: it's not hard to do and I bet that it could be done in under an afternoon of coding, testing and debugging included (these are just an animation table to add to the server side data for each avatar, and a few LSL functions to implement, to give access to the anim UUID entries in that table: dead easy !).
I never said it was an issue...
There is ZERO server side impact with the new LSL functions for animation overriding: the viewer-side AOs impact is in fact bigger since, instead of playing animations which UUID is loaded once and for all in a table of the sim server, the viewer AOs send stop (for the default anim) and start (for the overriding anim) commands to the sim server.
There is ZERO benefit to viewer-side AOs: please DO READ FULLY the message I posted back in 2012
and which was used by LL to define their implementation (they just opted for LSL functions to redefine the default anims, instead of a viewer capability and protocol, but server-side they use the exact algorithm I described): there are actually BIG drawbacks to viewer side AOs (no cooperation with Lockmeister "seats", and "lag" due to the "ping" time between viewer and server).
You don't need to have it in a HUD... Again, consider the Cool Collar example (i.e. the script can be placed in any worn attachment).
I beg to differ: an AO is dependent on what your avatar "wears" (is it a human avatar ? Male or female ? A furry perhaps ? Or a quadruped ? A mermaid, a naga ?), and as such it should be changed when you change your avatar's outfit (i.e. it must belong to a scripted object in each outfit).
There is nothing to reconsider. I'm sure you can take "no" for an answer.