[@rocketrobie2] Something I was wanting to say last night but I liked Momentum, I think considering both of there profiles they're going to be totally nerdy fan dorks for being in the Legion.  I do want to have Bulk Lad have a nerdgasm over being invited in by Cosmic Boy.

But going back to maybe a reason why another idea I was going on, and can still be possibly used by someone looking at this but undecided.  I was thinking Lyle Norg aka Invisible Kid would have a serious investment in this story.  As he would naturally have worked a ton with Brainiac 5 being a fellow super genius but in a much more creative and not calculating sense.  

But essentially for Lyle seeing everything happen to Brainiac 5 is a sort of feeling of helplessly watching your friend betray everyone.  I was picturing him just making a decent life for himself after everything but it's clearly still eating at him.  So with Cosmic Boy coming back and bringing the team back together.  Lyle joins because he feels like he has to be the one to 'put Brainiac 5 out of his misery' so to speak.