As long as they don't bork sideloading mods, I don't see a major problem, even if they kill the service. They will be able to offer model on console via their Paradox Mod launcher. It would cost them more to support Steam Workshop & console mods via a separate method.

Consider it against games with no official mod support - if they break your mods, you don't have a right to be angry.

While I think open and easy modding is an easy avenue to building a better fanbase and boosting sales, I also understand some devs don't invest in that.

Well, rocket league is a good example. They had workshop implemented by popular(well PC is <25% player base) demand, then when Epic bought them and become F2P, the Epic version does not support workshop maps and later requires modder to side load the maps in. Now with layoff etc it's even harder to ask them to re-implement workshop or modding support to the client.(they also announced removing player to player trade so it's a big mess there. ) So a game that supports it's own mod loading is a good thing, if the mod distribution platform is closing down, it's a lot easier to redirect the calls somewhere to load mod compare to steam integration. Say, if you buy on GoG or other platforms then you are fucked right?

Steam Workshop is several years broken for Cities in Motion 2 without any changes in Cities in Motion 2

As far as I know, the Steam workshop is just a convenience layer for mods, it isn’t a modding platform nor does it do anything to enable mods. All it does it give you a central place to apply your mods, and puts the files in the correct spot. Any game that primarily uses the Steam workshop can still be modded by manually placing mods obtained through a site like moddb. Many games with no Steam workshop support have third party mod downloaders/loaders which will do the job just fine.

I actually disliked the Steam workshop as a platform for CS1 mods because of the way modders can make their mods like building sets rely on 100 other mods like individual pieces. That practically destroyed growable modding for CS1, because the owners of the dependency mods either wouldn’t update them, or would outright remove them, so most of the dependent mods would be missing crucial assets and wouldn’t work.