I have on concern. The sorting hat only goes on people heads when they are 11, so what knowledge does it soak up?

 

I'll bet that every headmaster will put the hat on sometime during their time there.

 

Even if the hat once sat on the Founder's heads after they created it or on a single Headmaster's head at some point, you could claim it to soak up a fair bit of knowledge.

 

^Point.

And who's to say that various 'wise' people waaaay back didn't come to the Hat for council? I mean, it's a hundreds year old magical entity- it's got to have some grains of wisdom hidden in it's proverbial brain, right?

For the plot, this could be done Post-PS (SS)... where Harry just comes out of his first (well, that he remembers anyway) encounter with Voldemort. Obviously this Harry would be a mite more aggressive and intelligent than his canon counterpart, and so after Dumbledore decides to not tell him the reason Voldemort's after him, he in turn decides to find out by himself, or comes to the conclusion that he's the one to defeat Voldemort- why else would he try to recruit him so badly in the room with the Mirror? Or maybe when he hears the reason Quirrel is killed by his touch, and in conjunction Voldemort's power is overridden by Harry's, he decides he is the 'one'? In any case, he might turn to his other mentors- since Dumbledore is obviously holding him back and not going to aid him in his destiny (a bit of self delusion or the 'if you're not with me, you're against me' attitude might work well here) but they think that he's acting as, well, most youngsters tend to do at some point or another.

So where does he go?

The Sorting Hat- Harry obviously doesn't know about Fawkes yet, nor most of the bits and bobs in Hogwarts; so he goes to the only trustable intelligent entity in the school. Possibly with the Invisibility Cloak during the Leaving Feast?

This could turn out well if it's done right; otherwise it's just going to be an OC instructer that's named the Sorting Hat and looks like a tattered hat. And we know how many of those turn out to be good.

 

Not many sorting hat adventure fics out there. I read one a while back, was'nt very good..
Sounds interesting, could be good.