If they want to stick with the current dlc model, my stance would be to just release every dlc for free after a certain period of time, say 2 years.
That way we don't have 1000 permutations of the game knocking around depending on who owns what DLC, and instead of just 4 or 5.
And on a cost basis, with each DLC being on average 10$. A person who bought each DLC at release would have spent the equivalent of 4 times the cost of the base game. Given the game is 4 years old, mathematically it's basically the same as re-releasing the game every year with minor updates.
I think this would be better for fans, as if they take a year or two off from playing, and want to come back, they don't have as much of a cost in DLC to pay.
Also, I basically can't recommend this game to my friends to play, because the upfront cost of the DLC is too high. With the old DLC, they've already made their money, so I would just roll them into the base game.