Vapid, Declasse, Grotti, Schyster, Dinka, Crest have all appeared in official text for this game. That is six manufacturers confirmed to exist in this universe still.
What I do not know is whether the full roster carries over or whether they are rebuilding it. Bravado, Truffade, Pegassi, Obey and the rest have not been named in anything official for 6 as far as I can find. Has anyone seen them?
Nothing official on the wider roster. Six manufacturers confirmed by name is where it stands and I would not extrapolate from it, because Rockstar has retired manufacturers between games before.
Every previous game has quietly renamed or dropped a few manufacturers and nobody notices until someone makes a spreadsheet.
The spreadsheet person is always in this forum somewhere and I mean that with affection.
Oh that is a good catch. A branded kayak means the fictional brand layer goes deeper than vehicles this time.
Crest being in the list is the interesting one. That is a kayak, which means they are naming manufacturers for things that are not cars, which suggests the roster is being extended rather than trimmed.