Yeah, I know it exists. And before it existed you could hack up the 32-bit Flash to work in 64-bit browsers.
The point is, it being a PITA to use Flash on Linux never stopped many developers from creating pages that required it, so it's unlikely to stop them from creating Flash pages now.
You said "I'm not sure there's ever been an official 64-bit release" when there has been an official release for a while now. So you can understand why I might have thought you did not know an official release existed?
It has not been a pain in the ass on amd64 since the fall of 2008.
Is a trajectory issue. When flash was expanding the range of systems it could be run on, then the future looked rosy for it as a delivery platform.
Currently however it seems to be contracting on all fronts, while at the same time adobe is making life more difficult for the developers by giving them extra costs. So the trajectory really does not look good at this point.
The point is, it being a PITA to use Flash on Linux never stopped many developers from creating pages that required it, so it's unlikely to stop them from creating Flash pages now.