For my part at least, I have two scenarios in which Foles makes sense.
1)Reid loves the kid and thinks he's got 'it'. He doesn't feel like there's anyone in the draft that's any better and he's already got one year of tutelage with Foles, so it's a head start. You trade 1sts and get a 2nd/or give up a 3rd/whatever for the kid and don't look back. This is a Brett Favre to Green Bay scenario, not a Matt Cassel 2.0 scenario.
2)Reid likes the kid, thinks he's got potential but wants to stack the position, so he trades for him AND drafts the best QB available at the Chiefs highest pick. Depending on what you have to give up, that could be as high as #4 (a swap of firsts) or a 2nd. So it could still be Geno Smith/Wilson/Barkley/or Nassib/Dysert. If this happens, I think Reid's intention would be to have an open competition, best man wins. This is a less risky Seattle 2012 scenario.
And again, I still think drafting Geno and signing a crafty old vet is my preference. It IS possible, however, that Reid thinks a Nassib or the like is just as likely to work out for him as Geno/Wilson/Barkley (Ryan's numbers are good, he's got a gun for an arm and high intangibles).
It's all just speculation, anyway.