Thanks for taking the time to make suggestions! Great video mockups!
Also welcome to the modern Spine world! 😆 3.8 has gotten quite old. I hope you find the UI much improved, especially the tree and graph. There's a proper graph! Be sure to check out the favor tool, it's very useful for blocking out poses then doing inbetweens.
1) Hot key and method of screen selection of all child bones.
Double click is deselect and ctrl+click is multiselect. There's a Select - Descendant Bones
hotkey, is that sufficient?
2) Advanced bone splitting feature.
True, we should be able to do this in 4.2.
3) In Edit Mesh hold alt key to switch modify mode
I think we can do this, just need to double check that alt isn't already used for something. Right click cycles the tool, but it's not the same.