"The plan to cop millions of Pac listeners, you comin with me"
Eminem is a smart smart man. He already had commercial appeal and now he's alligned himself with 50 who has street cred (unlike Dre) and has adopted a new persona errily familiar to that of Tupac's (Listen to the end of Hit 'Em Up and compare it to Eminem on "Go 2 Sleep" feat Dmx). He shouted out all the hip-hop greats at the grammy's, most likely just so he could get respect he needs badly from non-white demographics (I'm sure he really did have respect for them..but combine that with having the roots perform with him) and beefing with Ja-Rule will no doubt attract more attention to him.
I'd hate to see it happen, but there is no doubt he's going to outsell everyone by the time he's done with rap.