Clipless pedals for wonky knee / crooked lower leg

I think the idea is that the zero float should click out earlier in the twist.

Yes that's exactly my idea, but I have to agree with:

And how exactly will the speedplays stop the feet from hitting the chainstay? If anything, will make the problem worse

As for

Well you can adjust float in each direction on the cleats. I kept clipping my ankle on my crank arms rather painfully, wound in the screw so my feet can float outwards but not in.

It seems that with Speedplays I'd have to limit inward float to stop my heel hitting the chain stay and crank arm, and also limit outward float to be able to unclip as my weird leg doesn't allow my heel to swing out very far. So it seems that I'd effectively end up with (close to) zero float anyway.

Pedal axle extender and blue cleats are on the way, will let you know how it works out.