Whilst you mention it (off topic to main thread, sorry) - two things that have come up in conversation recently were :
a) Ability to "refresh assets" in 3D engine i.e. reload models and textures without having to quit and restart the program.
b) Some information about or control of the connection between action and animation - i.e. currently the enemy receives damage from the 1st frame of the animation, so is damaged / killed before the punch is thrown or gun is lifted to shoot.
These might both be "big asks", but I see "B" as something that's probably necessary before the 3D stuff can really be considered playable. Perhaps if there was a way to assign the "shot event" to occur at a specific point in the animation, this would be quite easy to solve. There may of course be some other way of solving this.
"A" isn't necessary for a playable engine, but could make testing and development a lot quicker.