I actually ran into a few issues in the process. Recent versions of Urho3D ship with a Blender exporter to export directly to the files Urho3D expects, and it works very well for most things. But one thing it didn't seem to like, at all, was having my IK controls and posing bones inside the same armature as the deform bones that skin the mesh. For whatever reason, it just wouldn't export a functional animation with the new IK rig.
I ended up sorting it out, after some hours of despair and panic as I tried any number of combinations, formats, etc... I found that if I separated the IK control bones and targets to another armature (maintaining the constraint cross-links between the two armatures) then it exported just fine. It does add the slightest bit of work to the animation process, since I now have to keyframe two different armatures during the process, but that slight overhead is more than compensated for by the ability to IK my rig and make ostensibly better animations. I say ostensibly, because no number of clever IK rigs can really make me what you might call a "good" animator. I'm shite, it's true. I ham-fist GC into all manner of tortured poses, look upon my work and call it good. But it's not good. His idle animations sometimes look like he is reeling from too much goblin brandy, and he walks like a popsicle; that is, like he has a stick up his nethers. But still, with the new rig, it all does look a lot better.
The new retopo still isn't perfect; I'd imagine a real artist would be appalled. But it's far better than the old mesh decimate retopo.
That being done, I can bang out a couple more animations pretty quickly, so that he isn't stuck in the eternal walk cycle that he has been. Needed to do this to test out the action->animation mapping anyway.
Started redoing the character portrait widgets. Just a first iteration for now, need to rework the life bars and what not for use with the new UI system. That'll be a job for tomorrow, after I've done an Attack and Use/Loot animation.