Eminem won't jump in. His respect for Jada and Nas will prevent him from doing so. And Banks + diss tracks = wrong combination.
And, Ja stopped selling because Em, 50, Dre, D12, Trice, etc. dissed him to shit. So many fans think one of these rappers is God so if they say someone is a bad rapper then they'll believe it.
But 50 Cent alone versus Joe, Jada and Nas alone will crush 50. 50's only allies at this point are G-Unit, which they should check out the All Out War mixtape because they all got smoked on those tracks.