@EugeRe great work and post. I had not thought of using SSI for mempools. As you correctly point out the usage of zkps as representations of VCs is key.
The Ethereum Open Community Projects is about to publish a similar piece of work utilizing both DIDs and VCs and pointing out that most pieces required to implement SSI at scale with an L2 keystore actually exist today both as a global standard and as reference implementations. The draft of the paper is here in case you or anyone else is interested. Will update the blog site soon.
If you are interested in collaborating on this topic, let me know.
The report should be going