But this brings up that some Vim hotkeys are more positional than mnemonic (J-down, K-up), while others are more mnemonic than positional (I-insert, X-exterminate(?)).
This is why I believe that qwerty is the best layout. All applications have designed all shortcuts to be sensible on it. Any other layout is just going to be a disaster and negate any benefits and more during actual use.
You can of course use whatever layout you like and then while ctrl/alt/meta is pressed it switches to qwerty, doesn't save vim users though (or other applications where shortcuts don't need to be prefixed).
I'm not convinced switching from qwerty is that beneficial, I believe (but have not yet tried it) an orthogonal keyboard will do more than any layout will. But I admit that I don't have experience to back that up.
I've been using Dvorak for ~15 years now and the keyboard shortcuts don't bother me. For example, when Dvorak Ctrl+X/C/V is translated to QWERTY, they are in the positions Ctrl+B/I/(period). For shortcuts like Ctrl+C in Dvorak (Ctrl+I in QWERTY), I put my left thumb on Right Ctrl and my left pinky on the letter key.
Two minor problems, though: In Dvorak, V is immediately beside W. Ctrl+V means paste, but Ctrl+W means close window, so care is needed. And, any keyboard that lack Right Ctrl (e.g. the Microsoft Surface series) is an abomination.
The idea would be to optimize the keyboard around English (which you can't remap,) and then to optimize your editor keybindings around the keyboard (which are easy to remap.)
Positional key layout only matters pedagogically. I type dvorak and use emacs + evil (vim keybindings). To maintain the positional correspondence I'd have to swap bindings around and make my setup even weirder, so I just learned j=down, k=up, etc. Muscle memory doesn't care about rhyme or reason.
Food for thought.