Hi:

Ketron is probably the most use module and keyboard used THAT way at least in the Arizona state area, I know more than a dozen+ of profesional midi guitarist that use is like that.
In fact, there are 2 trends, one is like trigering chord changes from the guitar and with footswitches change the variations, fill ins, endings, etc....( the most popular use).
The other is to play the lead, there is this duet "Me and my Gal", my friends Phillis and Roy, she plays the chords in their SD1+ and he plays lead besides singing.
The models used to achieve this are:
Ketron XD3-XD9, X1-X4- SD1-SD1+ and the previous models like the MS 50-60 40 AND 100.
Hope it helps.