Well 3 parts should be possible, if they don't decide they want to rework the systems every game. Basically they have the engine and system, now they just need to be churning out assets, most of which don't require any creative input, simply remodelling based on the old concept art/the old game.
Probably still gonna take a while.
I guess it mostly comes down to how "full" these games will be. If they're 35-45hours RPGs each, I think it'd be worth buying but if they end up being more like 10-15hours, full price with a story I've already cleared before, I'm gonna pass until the complete game.
The timing in terms of consoles is also pretty bad, although I guess that just means they'll be re-releasing episode Midgard and maybe the next one too on PS6/XboxScarlet later on.