[ElProximo]

It is not impossible she could be signed up as Simon's replacement as that is a sort of traditional 'character' of the opinionated Brit,
and
Piers Morgan 'would've been' the heir-apparent but it turns out he is replacing USA Interview (presenter) legend Larry King.

But here is what you should know:
Cheryl Cole is UNKNOWN IN THE USA

The vast majority of viewers will have NO IDEA WHO SHE IS.
They don't know if she is a singer or actress or who she is?
They never saw her before.

Now that is fine and maybe she would be a good pick for replacement and do very well but just so its clear - she is a total unknown to that audience.