I agree with your comment, but how often does a high memory program get better at memory usage over time? My intuition is that use of resources goes almost exclusively in one direction. Layers get added, less often removed. On the other hand the typical RAM amounts in common hardware gets higher too.

Firefox did, while they did MemShrink project: https://wiki.mozilla.org/Performance/MemShrink. I note that Rust is in part developed by the same organization that brought a successful MemShrink project, so you should be more hopeful.

Nice. On the other hand, I feel like people will tolerate high memory usage in a compiler much more than they will in a browser. Memory usage in general is very different between the two - in a compiler it will perform many allocations and discard quickly, whereas the pain in a browser is more likely sustained memory usage from long-running instances.