Teensy is a good call.
PS Have you any idea how you are going to be saving settings?
For example, you may want to think of stuff in terms of banks and patches. Maybe each bank having 4 presets. If you then said had a support for 8 pedals with say, 3 variable controllers, thats something like 96 bytes of information per bank. Be wary that some microprocessors have relatively small EEPROM. For example, taking this example, that would give you only 5 banks. A lot of people will use a bank per song... so be mindful to get something that can handle this sort of memory requirement. This is also assuming fixed values... you may want some movement (which would be really cool and certainly something that I'd imagine would be really cool - imagine a tremolo effect for example, by turning a volume pot up and down)
Before going too far, get some requirements nailed down from the guys that are going to use this.
Additionally, been thinking about this, not sure that servo is the best option for this - you may want to look into stepper motors.
Shout me if you want some more info.