For all we know... since theoretically this product is called 'Labyrinth'... the adventure might very well still include Undermountain and a couple other FR-specific maze-like dungeons, in addition to whatever new trapped lair Acererak might have designed in Chult. I mean, this is in theory still an AP, so I wouldn't expect it to be just one single dungeon leveling a party from like 1-10 or 5-15.
I also don't think we should really be bothering to call it the "Tomb of Horrors"... because I don't think there's any way they're going to bother remaking the same exact "secret trap" dungeon they've done many times over and just putting it in Chult. The whole point of this type of dungeon are the surprises, which means using the actual ToH is counter-productive. So I'm guessing the only real connection to the original S1 will probably just be the use of Acererak, and thus the original S1 Tomb of Horros "remains" in Greyhawk. Instead, we'll get a whole new trapped dungeon that is inspired by S1, just like all the temples in Princes of the Apocalypse were inspired by the Temple of Elemental Evil but not actual duplicates.
I also don't think we should really be bothering to call it the "Tomb of Horrors"... because I don't think there's any way they're going to bother remaking the same exact "secret trap" dungeon they've done many times over and just putting it in Chult. The whole point of this type of dungeon are the surprises, which means using the actual ToH is counter-productive. So I'm guessing the only real connection to the original S1 will probably just be the use of Acererak, and thus the original S1 Tomb of Horros "remains" in Greyhawk. Instead, we'll get a whole new trapped dungeon that is inspired by S1, just like all the temples in Princes of the Apocalypse were inspired by the Temple of Elemental Evil but not actual duplicates.