I have thought about that type of solution for a second layer for quite some time now. I am not good at coding (I did some stuff using visual basic almost 20 years ago to solve a data storing issue where I worked at back then), but the issue that I was looking at regarding a 2nd layer was what consensus algorithm to use to determine which accounts have signing authority.
The only problem that I see is that needing multiple accounts to sign each transaction before broadcasting it to the core layer has some scalability issues (because of the time it would take to gather and process those signatures by each validator).
Having atomic swap capabilities on hive could be a posible solution..?