I have one question about the design. Let's say SVS is implemented, and I lock my ETH on Chain A. Do I need to specify on which Chain (B, C, D, etc.) I want to unlock my ETH just like I have with bridging, or - since these chains have a shared TX history, so I assume there's no double-spending risk - I can unlock it on any chain that's part of this 'SVS alliance'?

Yea I understand it to be the later but haven't seen much in the name of actual implementation details yet.

Good stuff! I wonder when we'll see the first people to actually implement something like it. I know that isn't exactly the scope of the article, but I think it'd be interesting to see SVS contrasted with the Chain Signatures approach currently tried by NEAR. Maybe another article ;)