The "DLC gameplay additives" is the only thing worrying me at this point. Whether or not it's free isn't as much of an issue has us receiving an incomplete game at launch. I would rather wait longer for the game to be fully optimized.
Yeah, cost isn't so much an issue (especially since I doubt they'd go that route.)
I think Tabata and his team are just feeling the pressure in regards of trying to optimize everything in-time; I'm assuming they've already got something like a projected release window and are trying to work toward that, but finding lots of difficulties in development due to FFXV's ambitiousness.
The "DLC" route is probably their "exit strategy" to alleviate that stress of trying to get /everything/ done, so that the team can focus more on the core aspects of the game and its story.
I'd rather wait a bit longer for an optimized product too, but I'd much rather have this option, than just having a bunch of content possibly cut-out of the game entirely.