Frogwares is now the sole publisher of The Sinking City

Not sure of all the details, but there was some big falling out between the publisher and dev and each put up their own version of the same game on several storefronts then proceeded to issue takedowns on the other version. Really curious to see what the contract looked like.

Yes, like SaturnArc said. The issue was between Nacon and Frogwares.
Nacon blamed Frogwares cause of the steam version of Sinking City cause it was buggy, lacked features etc.
Frogwares blamed Nacon that Nacon released the steam version without their consent, that frogwares did not develop the steam version etc.
But all of these posts, tweets are deleted. The issue was in court. And now this is the result.

Here's an old thread about it:
https://www.steamgifts.com/discussion/oIy8W/the-sinking-city-scam

https://web.archive.org/web/20200825181545/https://frogwares.com/the-sinking-city-is-being-delisted-heres-why/

https://web.archive.org/web/20210301202740/https://frogwares.com/how-nacon-cracked-and-pirated-the-sinking-city/

That's what I gather. You can start now, and finish until February 28th*. Or wait for the optimization and bugfixes and who knows what else - the update arrives at an unspecified "soon" date, I'd expect it within a week. (There ia no reason for them to postpone it, as the old saves will work for another 45ish days)

To me, it's like a cheating ex wife. Like yeah, they took half the money. But at least the guy is free from that bitch.
Maybe not the nicest analogy. But I feel like it fits.

I mean it's 90% discount. The new version according to the post link will be free for existing owners.
So like there is no reason to wait if you wish to purchase the game from steam. The only thing you have to be careful about is playing the current version now and not finishing it before February 28.

I would assume you get the DLC you already bought? Doesn't say anything about it being included in the new version that I can find, so I don't think any of that changed.

edit
Devs confirmed on the Steam boards that DLC just carries over, and if you already own the Necronomicon edition, you get the Merciful Madness DLC for free.