Steam version isn't updated.
If I understood correctly, the Steam version will update every 5 updates from the Patreon version, I haven't bought the Steam version yet so I don't know how far it goes, I think it might go as far as the beach arch, I don't know. Maybe the Steam version will update with the last update of the game before starting with the endings.
Is this game really worth developing for that long?
If the developer manages to get a good amount of revenue to sustain the project yes, it is worth it, although of course it all depends on the quality of the game.
I have seen some games that have been in development for 1 or 2 years and they are bad because the developer just made a couple of updates where they added some content and only fixed big.
While others that have only been in development for a few months are better managed to be long term development projects.
In the case of N_taii they already have a reputation to be developing a game for 2 or 3 years and know that the quality of the game will be good, maybe being developing a game for so long sounds like too much.
But nowadays even small games can easily take almost a year of development.
Bit of a silly question and probably already know the answer considering the endings labeled as "True Ending" in HC1 and 2 are probably meant to be the canon endings, but since the NTR Ending of HC 2 has the MC Noah sail away to this games setting, does he have a cameo in this game?
Well I think it's kind of hard to say, because the true endings of HC1 and HC2 were the least liked (which is why there won't be a true ending in HC3) so it's hard to say which of the endings is canon.
And the other reason is because if I remember correctly N_taii made it clear that although the games take place in the same world, they are separate stories that have nothing to do with each other, and the events that happened in the previous HC have no relevance to HC3.
The same example is what you say, in the NTR ending of HC2, Noah leaves in a ship, but the antagonists started as a kind of new kingdom and if I remember correctly and want to expand their domain, but in HC3 nothing is mentioned about that, and the same happens from HC1 to HC2, in the NTR ending of HC1 the demons invade the human kingdom, but in HC2 there is no mention of anything about that.
I guess N_taii made the decision to separate all the stories to avoid having to be careful to enforce "the canon of HC1 and HC2" where I guess it's up to each one to decide which ending is the canon, at least for me in HC1 I'll keep the NTR ending and in HC2 I'll keep the revenge ending.
But you are not wrong about something, there will be a cameo of two characters, one from HC1 and the other from HC2.