Thanks for the requests, definitely agree these would make great additions.
I think you could do this now (roughly) with a bit of work. The general steps would be:
- Put your physics items in a persistent symbol
- Make a custom behavior for the persistent symbol which runs timelines to change the bodies from inactive to dynamic
- On scene load/unload, trigger the relevant behaviors
As it is in a persistent behavior, the physics can continue to run. Clearly some of the physics might be a little off as it won't have velocity, but this might get you some of the way there.