XV is a unique stain in the franchise though. Everything else around it has released in a complete state even if I haven't loved the games themselves. I think they'll more likely go the route of sequels/part 2s in future if they want to monopolize off a single entry.
The last mainline (non-MMO) FF before it was a long time ago though. Things have changed a lot since then. SE now regularly release DLC and/or complete editions, FF15 isn't unique in that regard. Both World of Final Fantasy and Dragon Quest 11 ended up with improved "complete" editions. I think it's pretty fair to assume the same will happen with 16. It may not, but I expect it's more likely to happen than not happen.