I've only listened to one episode of Vox Cast, which one covers the statement that they will not be making specialized Primaris units?
I don’t believe the statement was made that they wouldn’t be doing them ever/at all.
There were statements about getting the releases of the basic units all out the door (and by basic, I infer that to mean the base ones - unadorned, not Chapter specific, etc.) first, with their plain armor, similar to how the original Marines were released, and then slowly layer on the details for veterans (and likely Chapter specific stuff) at a later time.
I believe it was in one of the VoxCasts with Jes Goodwin where he talked about the Primaris stuff, where it was going, how it is a reboot that isn’t, etc.