Can we have a 120 AP + 20%CDR item for champions with no mobility?

And how do you suppose that you'll be able to prevent champions with mobility from buying it?

I would rather the immobile mages see true buffs than to have to rely on itemization. Viktor and Veigar both already rely heavily on itemization.

I don't speak for the balance team, but it's actually really hard to design a meaningful item that we can actually release. We can have a goal of an item that helps champions without mobility, but drafting up the actual item is much more difficult than you'd imagine. If we had an item that gave 120AP and 20%CDR, what would separate it from Morellonomicon and Athene's Unholy Grail? If people continue to build those two items, then would they really build an item that gives 20% CDR and puts them over the cap? What type of passive or active would we put onto that item that is balance-able that players would really enjoy without breaking the game? Also, how do we realistically prevent champions with mobility from buying an item that is intended for champions that don't have mobility?

Actually coming up with good answers to these questions is pretty hard, and I've probably missed out on a lot of other questions that need to be answered before we can make a new item, which is probably why it takes so long to make new items in general.

I would love to see an item that is 120 AP and prevents use of any blinks/dashes by the champion when equipped (bonus points if it creates a small zone where no champion can use blinks or dashes). It'll never happen of course, but it'd be fun to give immobile mages an advantage over their mobile brethren.

there are plenty of low mobility champs that don't need this, like annie

Rylais is a really good item for immobile mages. It's core for Brand/Cass imo