Stardew Valley's creator thinks he will "always have a desire to come back and maybe add a thing or two", so we can probably expect to wait for Haunted Chocolatier for a while longer
Eric "ConcernedApe" Barone is obviously notorious for being unable to stop adding to Stardew Valley, but it sounds like he could do it even decades on.
I would not mind if these two games worked like Guild Wars 1 campaigns: you can play them separately as standalone games, but if you install both, they act as one game and you can play with the characters from one game in the maps with the other.