By all accounts, the HTC 10 is the best phone HTC has made in several years. Now there's another reason to get excited about it if you're the sort who likes to mod devices. TWRP is already available for the 10, even though you won't be able to get one in your hands for another couple weeks.
New phones usually have to wait a few weeks after launch to get an official TWRP build, but not the HTC 10. This custom recovery lets you flash whatever you want to a phone, including full ROMs. You will need an unlocked bootloader to replace the stock recovery. HTC supports that for the HTC 10, but it's unclear what the situation will be for the carrier-locked variants.
You can grab the latest TWRP 188.8.131.52 build from the official TeamWin download site. Maybe staring at that 43MB file will tide you over until the device actually starts shipping to consumers in early May.