Actually, 3D Blu-ray was full HD 1080p per eye, using MVC encoding. It is actually a rather well done format, in my opinion. If it was crappy, it likely would have done better (oops, I sound bitter again.)
As typical, for 3D TV the early adopter timing was a huge issue, as the initial TVs used active shutter glasses which are expensive and a pain, then passive 3D FHD TVs came out that used interlace polarizers and theatre style polarized glasses, so you got every second line per eye and only 1920x540. By the time the format was dying, the 2016 OLED I bought had 4K, so even losing every second line it is back to full 1920x1080, you could just use the glasses you had from the theatre, and it was so much better than the first generation that they are hardly even comparable. Between the mediocre starting TVs, the lack of early available titles and, more infuriatingly, the early bundling of those rare titles (specifically Avatar which you could only get if you bought a Panasonic TV or player, and Shrek which was a Samsung exclusive), it would make a great book on how to market things poorly enough to alienate even your biggest fan.
As for iTunes, I haven't checked many as I just discovered CheapCharts yesterday. I see most Marvel movies and recent Disney available in 3D (yay!), but I noticed some early Disney (John Carter) and Fox (Abraham Lincoln Vampire Hunter) titles I have on 3D disk don't seem to be out, yet, at least on the Canadian store. Not shocking, as Spatial video appears to be yet another different encoding format, so they would all need to be re-encoded.
I'm not sure even how to encode them, yet (though I haven't needed to, so haven't looked as hard as I usually would). I have created a few home movies on Blu-ray 3D, though, just for the heck of it, so I will be looking into what is required for AVP, so I at least have some idea when the time comes.