There are currently a number - 6 to be precise 
- of open issues regarding SeedVault:
Of those, it looks like 4 or 5 must be completed before SeedVault is working in /e/
If we look at #1675 Get SeedVault working with NextCloud backup, we see the most recent comments (in June of this year) saying
Manoj Nair @manojnair · 5 months ago
Hi @rhunault can we assign a milestone to it based on developer availability
Romain Hunault @rhunault · 5 months ago
@manojnair It’s in the roadmap, but not the highest priority right now.
So my guess is that it won’t be available any time soon, but if you enable Notifications for some of those issues you will get to see when (if) any further progress is made.