As a foe member I obviously have bias, but I don't see this becoming a rivalry in the true sense. I think it's either just gonna be sharkbrew flames with occasional shit in game, or it'll descend to aids mains fest immediately.
If it does become a proper non-cringe rivalry, I look forward to it, even considering the large amount of friends I have in FI (hopefully that's not impacted by team capes). FI are definitely stronger in CWA atm, but I think FOE even in it's diminished state has rather a lot of wilderness quality, and it'll just keep getting better as time goes on, and people come back/join from other clans. The pure scene has been awful stale for a while now, so hopefully if it does happen, this will liven things up a bit.