Sandstorm is an excellent project. I sort of consider it the platonic ideal of self-hosting software. It does everything the "right" way, especially with respect to security, but ultimately isn't compatible enough with the broader ecosystem for general adoption.
I've been wondering if a lot of self-hosting platforms are targeting the wrong level of scale. On one extreme you have single user instances (SUI hosting). The other extreme is centralized platforms like Google. I used to think the ideal for most people is the "nerdy cousin" approach, where each family has someone capable of running something like Sandstorm or Nextcloud. The problem is that I would much rather trust Google with my private data than anyone close to me. There's so much more incentive for them to go looking through my stuff. This makes me think SUI might be the way to go. Or maybe large federated providers, similar to what we have for email.