Making it backward compatible would very likely mean some limitations we currently have would have to stay in the sequel. If there ever will be PC2, I hope it won´t try to be backward compatible and rather try ti fix flaws of the current game properly...
Not necessarily. I'm certain it would be more work then just working with brand new components. I've never worked with the Cobra engine so I don't have a good grasp on the technical limitations of the current engine build. But I do believe it should be possible and honestly would be a huge selling feature for returning PC customers. Especially with visual upgrades.
Personally I feel like PC 2 will come if two conditions are met:
1.) The sales of PC source game and DLC have remained profitable for Frontier.
2.) The tech team makes enough significant improvements to the Cobra engine to warrant the PC dev team to start building new assets and systems from scratch.
Otherwise with the current setup of Frontier games, I feel Frontier will just continue to add features and content to the current Planet Coaster base game.