I really like Obsidian’s philosophy, and I would love to enable sync. I would probably subscribe to the service anyway to support the team, but I think supporting MFA is essential (with multiple Security Keys as the OP recommends).
Surprisingly, the feature is already available here on the forum (I have 2 YubiKeys registered) but not on the main service. The forum platform probably supports this out of the box, but the lack of strong encryption can prevent many of us from using Obsidian for anything serious.