we solved it in element x, but there appears to be massive inertia towards adopting it because it doesn’t have threads or spaces yet.

If I only use 1 device for 5 years, then lose it, how do I recover?

From a backup?

Backed up from what? People only use the cloud for backups, at which point the e2ee is compromised.

It doesn't matter what people are currently doing. In Matrix, there is a possibility to make reliable, encrypted backups. It can also be done with a simple interface.