it would be neat to have ability to preview how the mesh would look like on horseback animation(in fact it would be nice if it could be previewed in all animations, on and off horseback, 
)
If I understand your suggestion, it is something you can do already:
1- Locate the animation you want to use in your previews
(e.g. search for it with CTRL+F).
(note: in native, some of the animations used in the game are all put together in a big animation, e.g. "anim_human".
If your animation is in these, and many mounted animations are, then you have to right-click on it ==> [split with actions.txt].
This will break the big animations apart into the actual sub-animations. After doing step 2 below on the one(s) you like, you can just discard the modified animation file without saving: you won't need the split animations anymore)
2- Select the animation, right click on it ==> "Add To Reference Animations"
3- From now on, when you preview any rigged mesh, you should be able to pick that animation in the "Animation" drop-down list (inside the View panel)
4- Optional: later on, if you want to remove/change any animation in the list of "reference animations", including changing the ordering or renaming them, you might want to use: [Settings]=>[Edit reference data].
it is possible to have a replace fonction.
Reimport function: yes, actually this would make a lot of sense, and would not clutter the interface at all.
(Even if, sometimes, you want to re-import the mesh, but, before deleting the old one, transfer something from it into the reimported mesh -- e.g. color, rigging, uv-coords. This is because sometimes the imported mesh lacks a few of these data).
Edit: added in 0.0.77 (more info in
Update notes)
