The description of the Loyalist Edition on the BUY NOW! page states “First expansion when released.” This implies there can be more expansions - as long as there is a sufficient large audience.
We have been speculating about their new project in New Crate games. My thinking is, that they want to branch out, so that they have multiple revenue streams. Any new project should not directly compete with GD and its expansion(s). A different game will also enable them to connect to new customers, and some of them might take a liking in GD then, too.