Maybe the C-series fuselage but can you hang a wing on it that will give it the speed and range to compete with the 650?
On topic: If you can find a delivery position on a G550 in two years for $53M, take it and immediately sell the plane for $7M profit and buy a F900.
From what my previous employer says, a two year wait is doubtful unless someone gives up a slot.
Re: G550 brakes. They're a pain but not unmanageable. If you had a fix to make them smooth as butter all the time, do it. If it's a modest improvement, live with them.
Having come from an airline background, the G550 always felt like I was in one of those WWII submarines--constantly ducking into the crew rest to allow someone to pass. TC