Honestly I think the main thing ICs have lost is damage. In Melee / Brawl, when they get you (especially if it's a grab), you're taking a huge chunk of damage. Now that they've lost their fobble and everyone else has huge combos, they don't hit particularly hard anymore, and their other issues (limited range, weakened state when one is KOed, etc) now hold them back.
If you buffed their damage output a little bit across the board I think they'd go back to being viable.
And before people complain that this is purely theory fighter, ICs were one of my training partner's best characters in Brawl, along with Olimar and GW. His Olimar is somehow still pretty good in PM, ICs and GW not so much. I don't think I've lost to either of those two yet.