A lot of things "have happened". A few years back, I remember Parker defending Dirk for a stretch, in a regular season game. This was pre-season, and lots of unusual things happen in pre-season. I suspect it had more to do with Pop wanting to observe KA at the 3, and not Kawhi at the 2.
I don't know exactly what situations you think will benefit from having Kawhi at the 2 and KA at the 3, but if it "happens" in the regular season, it will most likely be from some odd-assed convergence of subs utions and Pop just wanting to throw a different look at an opponent. If it gets more than token minutes during the regular season, I'll be more than shocked. It's an aberration, at best, come the regular season. You and Apo are talking like it's some big thing to watch out for this year.
It's not that Kawhi can't play as a 2 - but it's probably not a good way to maximize his value. But Anderson's speed really limits him as a 3, unless you re-define what a 3 is. I'm not getting into any long-winded discussions about the whole thing, because we aren't going to see it enough to make it worth discussing.