MakerBot Industries

Servo drive-been there, done that! http://www.thingiverse.com/thing:6814
Yes, Gecko servo drives and a few others will accept the same step and direction signals as the steppers.

Bigger bot- suggest an Ultimaker style frame-did that with gen4 electronics
http://www.thingiverse.com/thing:10380
or on a Reprap
http://www.thingiverse.com/thing:8957

The bottom line is that you get into real problems using ABS a a material on anything much larger than an 8x8 build area. You material will shrink layer by layer and will curl. There is no beating physics and that's why there aren't 4x8 ft print beds.
http://www.freedomofcreation.com/collection/gaudi-chairs-3d-printed-furniture-by-bram-geenen

Notice that design purposely uses a shape that will not warp on the flat build surface, I would also think high tech material was used in a temperature controlled environment.

I'm not saying it cannot be done, just that it's impratical, your printed parts will need to be designed to counteract issues, and the last one, can your system run days at a time with no error in order to build something that large?