Haven't really thought of this much since it's still so early, but yeah, his chances seem pretty good at this point. If the Spurs continue to have by far the best defense in the league (and possibly one of the best defenses of all-time), that will do a lot to boost Kawhi's argument for DPOTY.
One of the main guys I considered a threat was Gobert, and now he's going to miss a good chunk of the season due to injury. Whiteside might get some attention. He's nowhere near the best defender in the league, but he leads the league in blocks and Miami is on pace to be a top 5 defense in the league. DeAndre will likely get some votes too, but I can't see the Clippers being good enough on defense to allow him to actually win it.
Honestly the only guy I think can realistically challenge him for it is Draymond. If GS can get back to being a top 3 defense like last year, I could see him winning it...especially since some feel he got snubbed last season (received the most 1st place votes but didn't win).