Looks like it's available on their custom hardware, but not as software only.
From the bottom of the page:
Disclaimer: Remix OS is only licensed to authorized business partners and pre-loaded on specific product models of those partners;it's not intended for personal use.
From the bottom of the page:
Disclaimer: Remix OS is only licensed to authorized business partners and pre-loaded on specific product models of those partners;it's not intended for personal use.