I don’t think they ever explicitly ruled out caching or pre-converting the binaries. And the module load library sounds like a generic conversion tool wrapped by an easy to use load module, not some inflexible black box.
This is squarely an OS problem. The OS itself will have to make tradeoffs between startup time, install time, disk usage, portability, and cache complexity with regards to member-conversion. And it will use the mill conversion tool as it chooses between them.
From a “just get something working” developer’s standpoint, wrapping the conversion tool by a load module is the easiest way to plug the mill into an existing OS without rewriting or authoring new major subsystems.
So, just chill and be patient. 🙂