Franklin Richards SHOULD be a teenager by now even by "Marvel time", but I think so may writers seemed to not really want to bother with a kid that he got sort of stuck and now he's perennially around 8-11. If he'd been in DC since the end of the 60's you KNOW he'd have served on some incarnation of the TEEN TITANS by now.
Speaking of FF continuity teenagers, y'know who may make a fun Runaway? Kristoff Vernard, who was once groomed by Doombots to be the heir to Doom and who was about 13 the last we saw him and has been in limbo for a good decade. So he could easily be in the same age range as the regular RUNAWAYS by now and could have some fun character conflict with Chase. But I'm just brainstorming here. Plus, as Victor was once believed to be the "son of Doom" for 1 issue, it'd be fun if they met the ACTUAL "adopted son of Doom".