A few streaming services have supported colorful high dynamic range video and ultra-high resolutions for a while, but Vimeo is making up for lost time in grand style. The company has added support for both HDR videos and resolutions as high as 8K. You're going to need a very rare 8K display to see footage in its full glory. However, HDR support is considerably broader: you 'only' need a device that can play HEVC video using HDR10. Some of Apple's newer devices (including the Apple TV 4K, iPhone X and 2017 iPad Pros) already do, and Vimeo is quick to point out that it's currently the only video hosting service to play HDR on Apple gear.
Conventional video is still available, of course, and you can download videos at their full quality (when eligible) if you want to share them or don't have the bandwidth to stream them smoothly. Vimeo is also promising HDR for more video standards (such as VP9 and AV1), so don't despair if you're relegated to "just" standard dynamic range.
This won't necessarily make a difference in your day-to-day viewing unless your favorite internet video producers upload to Vimeo. With that said, this could be important if you're the one producing videos. You now have another place to upload video at extremely high quality, and it will be viewable on more devices. Moreover, this gives filmmakers an easy way to sell these videos and otherwise put their best foot forward.