Maybe check out Fantoms programmable servos. Their website doesn't say alot about whats programmable, but when I talked to Troy (one of the owners) they are super adjustable like an esc. You can change the curve in the servo its self, speed and other stuff. I have 2 coming for my 1/10 stuff when they are back in stock. I'm excited to try them.

Fantom 1/8 programmable servo