AWS makes this impossible in a few places such as a fair number of ACM use-cases.

I think your cert-per-session idea is interesting. We’d need significant throughput and processing boosts to make that happen, probably at least on the order of 10X computing speeds and 10X transmission speeds across the board minimum. These operations are computationally intense and add data to the wire so, for example, a simple Lemmy server with hundreds of users slows to a crawl and a larger site eg Mastodon goes to dialup speeds or worse. You can test at home by trying to generate an x509 self-signed cert before connecting to a website every time.