I don't think it is a great concept to shut pro players out of online play. We pro players payed a lot for our instruments after waiting long for them , and we pay 150% for DLC with less functionality.
No one can expect people to buy pro updates when they don't have pro guitars. Since approximately 98% all of Rock Band players don't have a pro guitar, it leaves 2% of matches online, with a very low possibility of finding them online at the same time (since I am in Europe) PLUS having the unlikely luck of finding pro players who bought the same DLC as I did ....
Saying that you never planned online compatibility in the first place means that you never wanted to have pro players online. I just can't imagine that you didn't know how unlikely it would be to find a band with everyone having pro updates.
Pro Guitar is a great progress for this genre, but if this was really intentional, then rock band 3s online concept is a complete failure. Sorry to say so, but from all possible solutions, this is the most unlogical. Actually it is the most simple solution imaginable.
ANd there is one point that undermines my opinion on this: If I have only Drums, then I can still play with everyone else, since the guitar / bass / vocal / keyboard charts are included in the song file.
Why should this be any different with Pro Guitar? Charting it might justify addionional costs for those who play Pro Guitar / Bass, but it doesn't justify additional costs for everyone else. Specially with the Squier Strat in mind which only allows pro-gameplay, this is a bad decision. Imagine all those people that wait for the Squier. They will never ever play online, since they cannot find anyone to play with. I actiually never met anyone else with a pro guitar online. I am always the only guy with one.