In Fisher's perfect world (where they have a top 5 defense, a top 5 rushing attack, and best, most innovative special teams in the league), Foles is a perfect candidate to be the guy.
Is he ever going to be Peyton, Brady, Luck, Rodgers, or even Wilson? Probably not, but he might be Eli, and Eli has 2 Championships. Personally, I hate how "important" the QB is in the NFL. I think it is a bogus perpetual motion machine that ensures only super stars win championships, and only a handful of men in the entire world are able to play the position.
Someday, a coach (I thought it would be Kelly, but now I am not so sure) is going to bring an innovative spread offense to the NFL that takes advantage of above average athletes at the skill positions (which the NFL has in spades, and are quite a bit easier to find and draft) and doesn't require pro bowlers at 3 out of 5 OLine positions and a transcendent QB talent to win a championship. If the spread offense is responsible for more o linemen and QBs being ill prepared after they are drafted (which many higher level personnel people in the NFL are starting to believe more and more), then it make sense to tailor an offense that would take advantage of the plentiful WRs, RBs, and TEs coming out of college every year from all levels of collegiate football rather than suck for a decade + until you get a generational QB talent.