You still can't really buy one even if you've got money to burn, but the OnePlus One has official support for TWRP now. So at least there's that. In case you were wondering, the device codename is bacon. Obviously.
TWRP, for those who are not in the know, as the kids say, is a custom recovery that can be used to flash ROMs/ZIP files and backup a device. If you really want to get your hands dirty, a custom recovery like TWRP or ClockwordMod is essential. This image file is part of the v2.7 branch of TWRP, which is the current version for all officially supported devices.
It can be flashed through fastboot in a few seconds as long as you've got the bootloader unlocked. Now all you need is the phone. Good luck with snagging an invite to buy a phone. Which... ugh. Don't get me started.