You're better off buying the game on sale
Turn 10 Studios announced a Racing Game of the Year Edition for Forza Motorsport 5 by way of IGN, scheduled to arrive on July 22, 2014 for Xbox One for $60/£50/€70.
Given how much DLC there is for the game, you'd be inclined to think a decent amount of it would wind up included, but no, not really. On top of the core content, this package comes with the ten-car Top Gear pack plus the Road America and Long Beach tracks, and a third track that hasn't yet been announced. Thing is, both of those tracks can be downloaded for free.
Not a compelling enough offer, if you ask me. I get why they wouldn't want to include everything from the $49.99 Forza 5 Car Pass here -- there's money to be made, after all, and the content rollout hasn't even ended yet -- but don't release the game of the year edition so soon, then.