This might be a useful feature but I think it would be better to develop this outside the stdlib, especially when the mechanism needs application specific code (such as preloading modules used by a specific script).

If/when such a tool has enough traction on PyPI we can always reconsider including it in the stdlib.

BTW. Python runs on a number of platforms where a forking server (option 2 in msg322800) is less useful. In particular Windows which doesn't have "fork" behaviour.