We already have some storyline possibilities that Crate have mentioned:
12th July 2019 stream:
Any plans for the NPC found in the Fleshworks to make another appearance?
So his story is not going to finish with Forgotten Gods, his story is for things beyond. Which is more of a sequel.
19th April 2019 dev Stream:
gachibass_chechnya_kavkaz : Could you share with us what’s gonna be in the next expansion/GD 2 in terms of storyline/lore, at least a bit?
I’m not sure I should really talk about that because I’m not sure when or if it’s going to happen. I mean I can give you some ideas of threads we might pursue. For example there is the whole thing with the Emperor, the capital, with the Sun (son?), Ulgrim seems to be a special guy too. The Witch Gods seem to have gotten their way - what does that mean for the future of Cairn? What will happen to the future of Kymon’s Chosen? That Sigil?
1st March 2019 stream:
“Just in terms of the story to be perfectly honest I feel like to do the story justice at this point we need to do something much bigger than an expansion. And there’s all this stuff, those of you who are paying attention to the dialogue will know Ulgrim and the Emperor, there’s something going on there, the Emperor’s son, those are all big stories that would really need a lot of dedication to do them justice.”
Medierra’s also talked about why we won’t see a GD2 very soon in these threads: