Crossing my fingers that if we do ever get a Covenant followup, it is on screen and actually helmed by Ridley. I have no problem with adapting abandoned ideas into other formats (I'm really enjoying reading Pat Cadigan's adaptation of William Gibson's first draft at the moment), but so much of the appeal of Covenant for me lies in the execution of the material in the film itself. On paper, before the film released, I hated most of Covenant's core concepts – David as creator of the Alien chief among them (I ended up spoiling myself on just about everything in the film before its release, fully expecting to hate it), which left me all the more perplexed as I found myself sitting there in the theater, seeing the things I read and hated playing out... and loving them.
Then again, Gibson's Alien 3 is a script I don't quite like, and I'm having fun with the book as a sort of historical "What If?" so I guess a novelization of a hypothetical Covenant sequel would be better than nothing. I think I'd rather see a collection treatments, notes, "Ridleygrams," etc. though.