In the past i've been comparing this game to Cities Skylines and I still think this is a very great way to compare modern simulation games too. When we all grew up with the early Rollercoaster Tycoon and Simcity games they were the first ones of the genre. And I think in current year Planet Coaster and Cities Skylines are the only worthy modern games you can compare these too.
Cities Skylines offers an amazing base game with full steam workshop mod support and they released tons of expansions later on that people still bought. Because having this amazing base game with mod support just offers for unlimited replay-ability. Because it draws in so many fans and modders the game just keeps growing and growing. Many times PC games have been proven to be even better with mods and I think the next Planet Coaster should go for a similar approach.
The amount of DLC cities skylines DLC released after the base game proves how succesful PC sim games can be and mods only add to that experience. Now in the past I heard arguments against this because people thought it would break the game, or that the majority would not be capable of simply understanding this. Or arguments that it would stop the reason for official DLC to be made because mods would do it and this has also been proven wrong. The creators of Cities Skylines released more DLC than planco ever did even when they had full mod support. And the workshop system works great, I recently replayed it again while I only some of the DLC and the top mods are always updated because steam workshop is very decent organized and you could find the most used mods on page 1 or 2 anyway. I really believe the next Planet Coaster should go for this approach if they want maximum popularity for the base game as well the DLC. Because the real creators can always make more quality content than any modder can, since they understand the engine.
So for me: Mod support and Performance offers replayability so the game gains popularity and they can continue releasing quality content along with the modders long after it's release as it can really improve the game over years to come.
I also feel Planet Coaster engine underestimated a little bit how big parks could be. I think modern computers even on top hardware can struggle with big parks. So I think this is also something they have to look out for from the beginning so the game can grow without bottlenecking performance at some point.
Other than that: just offer a really solid base game. Exactly like Planet Coaster 1 but more improved on ways (like fence-tools or something from the start) to make things less tedious and easier to drop down and start playing the game. Also I think gameplay was a bit lacking from the start, you would get things like staff-centers overtime but I think the finances gameplay could also be improved somewhat.
Other than that Planet Coaster 1 is very good, it's just that it wasn't very future-proof due to having a bit disappointing performance and the lack of official steam workshop mod support. Doing this would make the game as popular as Cities Skylines and they got tons of official content and mods even being made today.