Fenix a.k.a Firefox Preview will not be Fennec 69. There are a lot of decisions the project hasn't made yet, but that one's official. It's an easy decision, too, given that Fenix won't have full feature-parity in three months and maintaining backwards compatibility to super old app versions is not worth it. The expectation is that users will want to migrate to the new store entry in the coming year or two.

As Ricky would say, "It doesn't take rocket appliances."