User blog comment:Xandermcc/Potential crossovers coming soon (SPECULATION)/@comment-24152851-20180216003445/@comment-24152851-20180216025702

Well it's either that or eventual leading on into Crisis on Infinite Earths. Superboy-Prime is just too heavily associated with those events to not bring them up. Wouldn't pitch it as being too crazy these days given they've got a transdimensional demon harassing the Legends right now.

Why J'onn though? I mean is Black Lightning set on Supergirl's Earth? I'd think a more local hero would fill that role.