Yeah, nice attitude... So basically i could also use unity to "mod" my own game.
For me vanilla is still a full game, and it should be somehow complete as a full game. It's a game, not just a construction kit to make a game.
Imho some total conversion mods did enhance the game much more than vanilla did. Adding mechanics, even graphical overhauls.
To be honest, i'd rather pay for darkness falls as a new game then paying anything for A19. Yeah, i know, i don't have to pay for any of them again, but what some modders did to the game is much more advanced that what TFP is doing atm.
Of course there is progress and not everybody likes every change, but basically 7d2d would have been worth selling every new major alpha for 20 bucks every year. But A19 then would be a version where i finally would say: I could have skipped this one.