As Tom says, there are a number of regulations that would prevent straight forward redevelopment. We have to remember that the reason a lot of clubs go out of town is due to space requirements. Not saying it's not possible as most things can be worked one way or another, but i'd agree with starting with the Merkland incorporating Section Y as a starter. Though I'd be very sad to see this being covered. Easily the most amusing place to watch a game at Pittodrie. Any development would have to be phased, could see 1/2 the south stand being developed at a time.
Tom's sketch was quite radical and would certainly like to think it could be considered, whilst rotating the pitch would mean we couldn't use Pittodrie during the initial construction, it could potentially work. SPFL being kind of course!