... This piece of the puzzle is easy and already well-understood. I had assumed that btc1 was going to insist on it's forking-block being over 4MB in weight, a simple and elegant solution to the wipeout risk.... They couldn't possibly be stupid enough to not do that, could they?
I believe that that is their plan, but there isn't a spec for anything that they are doing and that plan may not actually happen as they hoped so. Jeff Garzik has been repeatedly confused by/conflating block weight and block size such that the first time he tried to increase the maximum block size in btc1, he failed to do so because he had changed some constant related to block size not block weight. A lot of things in btc1 seem to be related to block size rather than block weight which is very stupid as segwit defines the limit by block weight and not size. So I wouldn't be surprised if Jeff Garzik failed to properly write code that makes a block have a weight greater than 4 million because he was thinking of things in terms of size rather than weight.