The specialization isn't necessarily load-time. I think they're envisioning it as most likely being an install-time process, so that distributed code is still portable but they don't have to worry quite so hard about the latency of the specializer. Ahead-of-time specialization will still need to be possible for creating things like bootloaders and OS install media.

I think it's safe to say that the future will have a lot of fat binaries.