To play it now?
I never understand comments like this... Stuff like "oh I'll just wait and get it for $10 in a steam sale in two years..."
We only have so many years to live... I don't get why people are so comfortable waiting literal years for things they could otherwise enjoy today... All to save literally like $30.
EDIT:
And I am not saying include all of the stuff in each subsequent release, I am saying support it from earlier releases if you own them.
IE: I launch the game and it reads my steam account and sees that I own the first game and a couple DLC for it... So the original factions and those DLC factions are playable in the second game for me. Likewise for the third game.