I think its a safe bet that Tomb of Horrors might be next, there is no other reason to relocate it to the Forgotten Realms.
I hope I'm wrong, because from everything I've heard about the tomb of horrors, its sounds boring as heck, trap, after annoying trap, after annoying trap, all over powered, no real plot, no interesting characters, I can think of a campaign that sounds less appealing honestly, and ITS A LOCATION THAT BELONGS IN GREYHAWK, although its good to know Toril traded comingling with Abier during the Sundering, for comingling with Greyhawk. Who knows maybe AO screw up abit during the Sundering and parts of Greyhawk got sucked into the realms, confusing both worlds.
I know next spellplague parts of Toril can switch places with parts of Greyhawk. Suzail, the capital of Cormyr can trade places with the City of Greyhawk!
And parts of Athas can trade places with parts of Abier!
Okay I kid. I hope.
On a more serious note they are literally ripping dungeons from other worlds to dump in FR, that is how unoriginal they're getting. Sigh.
I will say the thinning between FR and Greyhawk could have interesting reprocussions, but they'd actually have really explore that. Are other parts of Greyhawk shifted to FR?