My account on the forums is over ten years old now
If the amount of time needed to make the mod is much more than 6 months, then I think there's a lot of worth in releasing a demo before it's done, because waiting all that time with little to no community engagement can be exhausting.
it's always good to release a demo, even if it's just asking a friend to playtest it - that way you get a fresh experience and realtime feedback/bug reports