Controlling the TLD has its own benefits and drawbacks (managing email reputation, for example) but as a regular person I have more reason to trust `.cloud` than `.self` purely on the basis of proven continuity. My `.com` domain will almost certainly live as long as the internet does provided that I keep paying to renew.

Regardless, a UUID is probably the right call. It doesn't help with memorability but it's at least more stable than an IPv4/IPv6 address and can be hard-coded. I wonder if you would get a full zone or if it's just an A/AAAA record given their broader goals of email and VPN tunneling.