The way that I can think of doing it before it is implemented into Itch.io is top make a 'Gold' Edition of the game with all the DLCS so the consumer starts to trust you and doesn't think your a second 'EA' ( Electronic Arts ). Get the trust before releasing 5 copies each with a different DLC making them pay for the base game and the DLC each time they buy your game. To have multiple DLC make a Silver , Gold , Diamond , ETC. each with more and more DLCS and benefits but warn the consumer that the edition contains the 'BASE GAME'. This could also help with branding by making special banners and in game benefits so if the player wants to they could buy just the base game. and If they want a special thing ( Skins, ETC. ) Then they have to get a better version ( TF2 Premium ). BUT DO NOT DO WHAT EA ARE DOING. DO NOT LOCK ANYTHING AWAY FROM THE PLAYER OR THE TRUST BETWEEN YOU AND THE PLAYER WILL BE BROKEN AND YOU MAY NEVER SEE THEM AGAIN... EVER.