I think you underestimate the importance of the role he's expected to take. The keepers who are comfortable with the ball make it look easy giving the impression it is. Nothing could be further from the truth.I honestly can't imagine this is the reason he can't fit into a Guardiola team. You'd think Pep's teams have keepers doing some fancy footwork - they don't. Neuer made a bit of a habit of coming out of his box to sweep up sometimes, that's about it. Joe's perfectly capable of passing a ball out from the back - by foot or by hand. If the rumours of Guardiola not fancying him are accurate, it's probably for other reasons imo.
Could be his distribution / attitude / decision making or number of other reasons, but would Pep really ditch a keeper purely because of a lack of finesse with the ball at his feet?
The whole system breaks down if his keeper isn't keeping the game flowing.