My suggestion in a fly-by wire avionics system, and I'm not referring to SAS. It could be implemented into stock or made into a mod. This way an aircraft with, say, a broken elevator or missing canard, could fly. Heck, if the system were properly implemented, you could fly an aircraft that is facing backward without the control surfaces going the wrong way, or even fly an inherently unstable aircraft!
Some background info (especially for those who don't know what an actual fly-by wire system is):
TL;DR: Instead of the aircraft responding to the stick being pulled (or in this case [ S ] being held) by deploying elevators, the aircraft just calculates what control surface movements would actually accomplish this pitch up.
Here's a hypothetical situation to demonstrate what I mean:
You're flying an F-16, but (oh no!) your right stabilator isn't moving, no matter what you do. Now, whenever you try to pitch up, it also rolls the aircraft left. A fly-by wire system would accommodate this by also using the ailerons to stop the roll before it even happens.
you're flying an Aeris 3A (modified to be supermanueverable), and now after pitching up to vertical, you have stalled, but your attitude is still nose straight up. You try to pitch back, and the canards face leading-edge up and the elevators face trailing-edge up. When flying normally, this would do the right thing. But because you are falling backward, it causes a new pitch down. Similarly, roll is also reversed!
To simplify it further, the fly-by wire system makes it so that the aircraft does what it thinks you want, instead of what you asked for.
KSP could gain so much from a fly-by wire system. Even if you don't fly aircraft, it'd still be useful. Vertically landing rockets would be so much easier because you wouldn't have to fiddle with a negative authority limiter on control surfaces.s2