That's true, although it seems like a lot of those apps might not use MapKit in a way where its use is a problem, right? Apple's maps probably works okay if you already know where you're trying to go. It's location and directions and such that are the problem.
Google could be well be working on a drop in MapKit replacement as well. As least I would if I were them.
That would require the developer to rebuild their app with the Google map in there instead of (or as well as) MapKit which, will possible, seems unlikely for most apps.