WILL L4S/L5S COME NEXT? WHERE DOES THIS END?

Summary from the TLDR Crypto newsletter

Though onboarding and transaction costs decrease by 99% for L3s compared to L2s, the reduction in higher layers is not nearly as significant. L4s and up improve scalability but ultimately settle to Ethereum and do not come with additional cost reduction. There may be L4s that emerge on the most successful L3s, but primarily for ecosystem reasons and not technical or financial benefits.