There’s a number of things you could do to bearer thralls to make them relevant, ranging from the very ambitious stuff like in the OP, to the easy (if boring) stuff like (further) increasing the number of slots.
I can’t speak for others, but for me personally, even with the increased slots from the latest patch, bringing a Thrall with me is not worth the hassle, not even close. I have to constantly babysit them so they don’t kill themselves, avoid elevators etc.
I mean I’m free not to use them (and I don’t) so it’s no big deal, it just seems a bit wasteful to have a whole class of thralls whose only function is providing a backpack.