The problem with GT Sport adding paid DLC is that it focuses mostly on online play. So what happens when GT Sport has 5 DLC tracks? Are they going to use them in FIA events? So people who don't buy DLC aren't able to participate in a chunk of FIA events. That's not even pay to win that's pay to play, that's even worse. No big deal for casual FPS games and what not, but if GT Sport is giving away prize money, and trips to participate in World Tour events and Finals, then everyone needs to have the chance to participate in every race, not just those who pay for DLC.
That said, if they add DLC packs that you can only use in SP and private lobby's then I won't care, I won't buy them anyways.