The machine design is all about balancing compromise. From an electrical power drive to the motor what you propose (locating the drivers close to the motors) is a good idea - you're removing parasitic resistance and impedance from supply lines to the motor - which will impact the performance of the motor at speed. You're having to balance this with driving the digital step/dir signals over a longer length of cabling, and these are more susceptible to noise, but it's not rocket science to switch these (non-linear) resistive loads of a few volts / milliamps at 200kHz - differential drive is nice but not necessary unless you have long cable runs and a high noise environment (and you're removing a good proportion of the emissive lines by removing the high-current AC signalling to the steppers). I'd invest in a heavier gauge power cabling to the driver.

The other compromise is the mechanical aspects, and as others have said - vibration, dust etc. You are making life difficult for yourself here but this is just part of the overall design compromise.