Lend me your brains

If I use front brake in a skid I normally (always) fall off.

You will have 2 different chain lengths, which, all things being equal, will mean one side will wear / stretch faster than the other. So if you do manage to get the rear wheel straight in the dropouts after a couple of months I would imagine you will struggle to. Perhaps the effects of this won't be noticeable.

Good point on the wear and tear. I might make the chain length equal if I can.

I can't get my head around why having different ratio forwards to backwards won't work, seems possible but perhaps not practical. I do wonder if it's possible that the pawls in your freehubs could lock to oppose each other and not allow the cranks to be moved in either direction. I'm not too sure. {edit - this is bollocks}

Definitely bollocks ! ;p

There is no information (in a technical sense) communicated between the freewheels, they are doing only what any other freewheel does, freewheeling or driving.

Try it! Tell us what happens!

Once the wheel is locked the gear ratio is irrelevant. Have you tried leaning further forwards?

Agreed, once the wheel is locked the ratio is largely redundant, but lower ratios make locking the wheel up easier and that would be the point.

Also simple modulation of the rear wheel speed would be easier on a lower gearing.

Tried leaning forward more, and it does help, but less than ideal and still not enough control for me.