Does the game need a new type of CC to deal with mobility?
Our current counters to mobility are Silences and Roots. There are minor problems with that.
Silences stop mages from being able to cast any spell, preventing them from defending themselves, and wouldn't stop a Kalista from dashing. Roots stop everyone from moving, immobile champions or not.
If these types of CC are delivered instantly, the cry is made "No counterplay!" but if they're not instant then they will hit immobile champions more often.
So what if there was a new type of CC that disabled mobility spells/passives, but still allowed people to walk and cast other spells? Use it on a Ziggs and he can't activate his Satchel Charge. Use it on a Jinx and she slows back down to normal after killing your teammate. Use it on a Zed and he can't dash back out after bashing on your Death Marked face. Use it on an Annie and prevent her from Flash-stunning you.
I think this is the type of CC that could be the counter to the mobility creep. Yes, it would be hard to add to older kits, but reworks happen.
I'd be much more confident in PBE Veigar's E if it had this type of CC slowly expand from the center to fill the cage, hitting the wall when the stun goes up. The CC would also help it feel like an actual cage, not something to just blink out of.

's Gravity field stunning them for depending on how many stacks they have (.5-1 seconds ultimately as 3 stacks would stun) would be a cool addition to a strictly CC ability.Thinking along these lines adding similar things to CC only abilities would be kind of neat, perhaps dashing into
's glue roots you small bits like that would help put mobility in a better spot.