Dizzy Mizz Lizzy  Dover  Guano Apes  More Miley Cyrus
 The Rasmus  The Veronicas  More Volbeat
My original solution when this issue popped up was to one lighter the songs and then go back sometime and play them on regular drums, but I have found that when I have over 1,000 songs to choose from that have proper pro drums, I have no desire to go back and play songs in regular drums. It's a shame that we can't get the same value out of early RBN songs like we can out of early HMX DLC, but that was Harmonix's choice when they decided to keep pro drum authoring secret until after they had announced Rock Band 3.
And besides that, the one lighter rating is not necessarily a good solution for people that play multiple or all instruments, because they might like the song other than the non pro drums compatibility.
Also one lightering the songs doesn't seem too fair to the artists, since those ratings actually get averaged into their rating on the marketplace