Hello - the underpinnings for most, if not all of what you are asking are there in V7. Commands, not at already for prime time, like 'testFilletSrfNonRational` have provision for Bezier segments, control over the rail structure etc. Note this command is very unstable at the moment but just to give you some hope. I would love to get these sorts of features properly into a more comprehensive filleting command much as you outline. That said, I am not waiting under water.
-Pascal