Why not permit a hard quota on an NSF, and make that it's *starting* size as well, so no new OS-level allocation has to occur? I can think of many cases where I'd like to say "make this NSF 100MB, no matter what data is in it. Just pre-allocate the file space to avoid OS fragmentation."
It would be great if that were bundled with COMPACT in some way. "load COMPACT my.nsf -f 100M" sounds like a great example.
It doesn't have to be a permanent setting for all replicas of that database -- just an aspect of the ODS. And then you can do quota-style warnings as the allocation within the file approaches the fixed size. Once it's there, you treat it like an absolute quota limit.