This is actually the last expansion for it.

They have said they’re doing Grim Dawn 2 but it’ll be quite a few years until it’s out (like 2030+). They’re working on an RTS set in Cairn (the setting of Grim Dawn) which they’ve developed their own engine for. While working on that they got the itch to do one last expansion for Grim Dawn. Once the RTS is done they’ll fork the engine to make Grim Dawn 2.

This is from an interview that Chris Wilson (of PoE fame) did with Arthur Bruno (CEO of Crate Entertainment who make Grim Dawn).