The resolution can get higher, easily. Use a scaled resolution (above 1440x900) and the game can run in up to 1680x1050. In my testing, it won't run 1920x1200 or 1920x1080 if the scaled res is set to 1920x1200. No idea why. If you use SetRes, you can force 2880x1800 and the game will run at that res.
Unsurprisingly, the game is actually playable on "high" (the equivalent to the PC version's medium, to be blunt) at that resolution. The reasoning that Blair gave isn't actually an excuse, it's just a roundabout way of saying that Aspyr haven't bothered enabling those resolutions despite the fact that they work just fine on a decently outfitted 2012 15" rMBP or later.
As for higher texture quality and the like (assuming it can be done), they'd probably have to release an update that includes OpenGL 4.1 support. That was supposed to have come with the Burial at Sea Part 1 release, but there must've been some miscommunication because that didn't happened. Hopefully it will come later.