Regarding the small size of the YRG:

My guess is that they were originally just aiming at the kids playing Guitar Hero (as it is also a game controller)and maybe unexpectedly came up with technology suitable for a full size once they saw serious musicians going for it also.

According to the $500 pledge promotional for the first 100 people (aimed at raising $$ for the development of the YRG PRO) it will retail at $899.

"YRG-Pro | Innovator Special: One YRG-Pro in black or white. Gig bag included. $899.99 Value "

Just a guess.
Carkins