We are haunted by dead futures that cannot come to pass.
If anyone wanted to keep track at home, 3Whysmen summarized the timeline neatly in a post on the subreddit:
This is from X7, which wasn't Disco Elysium 2. Disco Elysium 2 was Y12, Y12 was cancelled when Kurvitz, Hindpere and Rostov were fired. X7 development began after that firing and ended after the mass firing where Tuulik was let go.
X7 was supposed to be fairly far in production when it was cancelled and supposedly had a playable alpha build that was circulating on a USB at some point. Where as the cancelled sequel Y12 didn't seem very far into production when it was cancelled.
Also, that this surfaces when Tuulik's NDA expires and he gets to start working on whatever it is they're working on at in Summer Eternal... let's just say that there are no such things as bad coincidences.
For what it's worth, I'm not sure how I feel about what's presented here: a lot of it reeks of sequelitis and a "more for the sake of more" narrative/design philosophy that... I feel kinda misses the point of DE's elegant mechanical simplicity and how those mechanics reinforced the narrative being told. Of course, we can never actually know if that was actually the case, since the moneymen strangled this in the crib.
But maybe it's better that way- the Disco Elysium sequel in our mind will always be the best one.
Edit: Derp didn't realise CredibleBattery also posted the link as well but I guess I'll just leave this post up cos I don't want to delete and type everything again 
I honest don't think Disco Elysium needs or should have a sequel.
I think that if Kurvitz, Hindperre and Rostov wanted another crack at telling a story in their world, I wouldn't be opposed to it. But only if they're the ones telling that story.