Still no progress in the Pose Editor part, so can't say how hard or easy this would be.
What I can say is that in Unreal the pose editor is truly advanced, comparing TK17 to Unreal Editor/Sequencer is like comparing Microsoft Movie Maker to Adobe Premiere.
Not sure if I got right your question, but I dont think that it will be easier in Unreal to make what you want (as an amount of work). What you could do in Unreal would be to have the poses separated as animations and in timeline you would just swap actors or move the tracks as a whole or only a portion of it maybe directly to a different actor.
Unreal makes things easy, logical, you get some nice explanations why and how something works, but you still need to learn that and get the hang of it.
So far I've been talking only about Unreal Editor/Sequencer which is not a game but a game engine editor, it comes with its own licensing (for developers, is free to use) but is not for the masses.
Unreal Engine can do impressive stuff like below, but again, this is Unreal Editor/Sequencer, is not the game I'm working on. This is still something I need to figure out, but I'm not excluding the fact that the game will be one thing but in order to make good poses and animations then people will need to use the Unreal Sequencer/Editor if they want full freedom.
I will first try to bridge the gaps and provide all low hanging fruits features, models, basic animations, etc. If people want more, then they can use everything I will provide as the base and continue from there to make their poses/animations, mods, etc.