The same problems with closing Guantanamo Bay still exist today that did during the reign of George II. Prisoners need a trial and, if convicted, need to serve their jail sentence somewhere.
The latter, in my mind, poses the biggest roadblock to closing Guantanamo Bay. No American wants a convicted terrorist in their neighborhood prison. Instead of NIMBY activism against the green agenda, we are/will be faced with NIMBY activism against convicted terrorists in the local maximum security prison. Local, of course, meaning rural since most maximum security prisoners are not on Park Avenue surrounded by a major population, which plays well to the base of the GOP.