The installer doesn’t build from the AUR, it builds from the official arch repositories, and while I guess they could make a script that would build from AUR I’m not entirely sure that’d be part of the Antergos… [i:mqoupk3x]philosophy[/i:mqoupk3x], I guess.
If the Pantheon team creates a stable binary and it gets included with the community repo though, I’m sure having it as an installation option could be quite possible. In my experiences however (a few weeks ago) it was extremely buggy. Indicators don’t work correctly as they’re dependent on Unity-specific methods, and at one point the pantheon-greeter broke my lightdm entirely to where I would only see a black screen after choosing antergos from grub. (I never did manage to fix that, wound up reinstalling. I wasn’t impressed.) And yet apparently I never learn, because I also tried it on a laptop of mine with Manjaro a few days ago, but once Pantheon loaded you were unable to logout/reboot/shutdown unless you used the terminal command to power off the system, and I also couldn’t find any settings for… well, anything, aside from “Desktop” which changed the wallpaper.
There’s still a long way to go before it’s stable enough to be included as an installation option.
As to DE support, I don’t really think there’s much “special care” needed for each DE actually. That implies upkeep of some sort, which is up to the user, not the Antergos developers. There’s certainly some [i:mqoupk3x]work[/i:mqoupk3x] that needs to be done creating the installation scripts and making sure everything goes through alright, sure… but we’re not like Linux Mint or something, where they’re basically overhauling Ubuntu every release to ensure their DEs still work. Because arch is a rolling release, it just doesn’t work like that.