Yes, I've often considered that this is probably how Java's collector tends to behave in practice, particularly with the eden and young generation. If you're handling an RPC call that returns promptly, it's probable that all of the structures you've allocated on behalf of that call will be part of the young generation and can be efficiently collected.
Indeed, it's one reason why I've assumed that Rust's memory model might turn out to work well for services (not having had a chance to try it): there's a clear entry point where the request begins and ends, and all of the memory allocated from that point onward can be discretely tracked and freed upon completion. In the services that I've built, the majority of the allocations are for these short-lived objects, with a relatively smaller amount being related to long-lived objects like connections to other services or caches. I imagine that websites and services might behave like this, though I haven't studied it carefully.
I'll be interested to see how transaction-specific optimization turns out, and whether it can do better than a general purpose generational collector.