As soon as I settled on Babylon.js I found a viable process for exporting models with multiple animations from Blender in THREE.js.  The glTF exporter for Blender now experimentally, but officially, supports multiple animations.  I created a testing scene then used a very basic rigged human from opengameart.org and made some intentionally terrible animations.  The animation names (like “walk,” “run,” or “sit”) export correctly and they seem to play correctly too.  So it looks like I’m back to THREE.js.  The only real downside to this is that I’ll have to tackle collision detection again.  I don’t really want to deal with collision detection, but at least I’ll have the chance to optimize the system so that it behaves they way I want and doesn’t waste resources calculating things I don’t really care about.  I made more progress on the game using THREE.js than I ever did with any other library, so I’m actually excited to be able to start using it again.  I’m basically going to pick the old code base back up and just tweak it to load glTF files for pretty much everything.  That will take me a while, but hopefully I’m back on track.