How close would you say the game is to completion?
Is it worth it to hold out for a bit before trying to play it all at once,
or does it still have years to go before the final update drops?
How close to completion? Not anywhere close! The game is still introducing characters when it finishes the current content.
It sucks, because this was a good game. But it's probably dead. I guess the dev promised to come back when he no longer feels burned out, but there is no guarantee that will ever happen.