tl;dr
They need to go to an F2P model for maps. Sell armor, weapon skins, and visors. Give these in exchange for paying for the maps. Everyone else can just freely download the maps.
This way the population stops being split and people that pay for content can actually play said content. Because it seems DLC hasn't been really working out since people actually had to pay for it. Even Halo 3 didn't hit majority DLC adoption until the Mythic Disc, and the chance to reunify the Reach playerbase was shot to shit with the car crash that was the Reach Anniversary Disc (oh hey, now not only have we split the playerbase with DLC, now we've split it depending on which disc you're playing from!). Could have made it a full Mythic style disc (yes, I know it was to keep it under 60$), DLC adoption in Reach would have exploded. The Anniversary disc still pisses me off, if you couldn't tell. The most ass backwards release in terms of design and commercial intent.
edit: I made these for another thread. Clicking the things will take you to the DLC content.