Just because I did a little googling, I'm not claiming to be an expert, but I got from just about every article I read on the subject, that it depends on what kind of photography you do. That sRGB is the standard for web photography and even certain types of dead tree publishing, and has an easier workflow, while aRGB really only shines with specific print photography (portrait and fine art photography commonly being cited, though there's even debate about how much of a practical difference it makes), is useless for web photography, and requires a little more work for the best results. That's why I think it might be beneficial for the OP to be a little more specific. I may not understand all of it, but when I read photography pros talking about this stuff, they generally seem very specific about what they require and their workflows. And again, not trying to start a debate or anything, because I don't know enough to respond.
I guess I don't understand your point about 27" 4K monitors. They're like regular 27" 1920x1080 or 2560x1440 displays, except really extra sharp. High megapixel photos and 4K video look amazing no matter what the HiDPI is set too. You can set it too 3840x2160 or 1280x800, and a photo will have essentially the same on screen pixel resolution (i.e. 4K). I admittedly don't have a 27" Apple TB Display to compare it to, but I can compare it to a 30" Dell UltraSharp U3014 2560x1600, which is also a fantastic display.
I'm sure 32" 4K displays are great as well, though having used 30" displays for many years, I think 32" might feel just a tad big for me personally. But maybe that's because I've never had one. I have friends that have a 32" tv set and sit across the room from it.