There are several requests for something along these lines, but several of them could be solved by changing the animation system as follows:
1) Remove the "emote" animation override time limit. It is currently 10 seconds.
2) If a user locomotes (as in, hits WASD in Desktop, pushes their Vive pad for movement, moves their Rift analog stick for movement), then cancel the animation and revert back to the initial state.
Use cases: Custom AFK animation, long dance animations with music, long "transformation" animation with particle effects and other fun stuff, etc
As a P.S., an additional "category" of animations that could be toggled on/off would allow for things like swords, guns, objects to pull off your belt, paletteswaps, etc.
P.P.S-- these ideas aren't 100% mine. I've amalgamated a lot of them from other suggestions into one general suggestion here.