So I'm nuts enough to think about this but I finally put it all togeather
If i could mix and match SR it would turn out something like this YMMV

1e - Decking, Initiative
2e - Skills, Defaulting, Combat (minus Initiative)
3e - Character Creation, Dice Pools
4e - Magic and Rigging

Granted there would have to be some house rules to tie it all together but I think each edition had some things right.

just the $0.02 of this old grognard.

You missed something. Fixed or Variable TN?

Yeah I know, I like both... Variable is a blast when its high (say 20s and above) and someone makes it (table screams!)
Fixed with Variable Thresholds is way better 80% of the time... + Auto Successes are good for Knowledge Checks but its missing that big table cheer and tension as the die gets rolled up. Will they make it or fail?

Oh and I would pick pre 4e attributes.