A Mercurial for AP users.. Why or why not?

An idea that's recently crossed my mind is having a that builds into an but instead of AD stats, gives AP?

a quick FAQ: "Why not get a instead?"

Should I find myself running into more AD than AP on the enemy team and if they carry a lot of cc, I'm either wasting 1/2 a slot by never upgrading or buying and not necessarily benefitting from the itemization. Also, being able to choose what CC you QSS can be really important as far as lategame teamfights are concerned. I don't see this item being an early-game/mid-game rush, but it gives mid-laners a purpose to buy QSS for later, instead of knowing they're temporarily blowing gold they'll probably have to sell for Banshee's or a late-game AP item.

The only reason I can see this not having been made already is perhaps that people want CC to be the way to immediately shutdown midlaners such as or , who are naturally immobile in exchange for damage output. But, people want that for their adc marksman too, and with the same idea of putting out damage and being squishy I'd really like to have a way for an immobile midlaner to to defend oneself, just as I'd buy QSS if I wanted defence as an immobile adc marksman.

The only way to do so currently is to take , which doesn't even take off as many forms as CC as and for a summoner spell slot, that really feels lacklustre.

I'm looking for opinions on how the community feels about it and why/why not this would be a positive/negative addition, so please feel free to speak your mind! Turn your downvotes off, boys.

I'd totally understand if this was just one of those things they wanted to keep exclusively just like is for mages, but I was just curious as it bugs me every now and then, being unable to save myself from instant death.

A/N: I have not included a poll as I want opinions on why/why not you would agree with the addition of an item like this, instead of just yay or nay.

Thanks!