The jar files used to be memory mapped, and as far as I'm aware they still are. So there should be a noticeable improvement in seek time by eliminating never-used files.

You could also perhaps be looking at a situation in the future where the JRE can selectively exclude things at install time, which would be nice.

Clear, but the single rt.jar will be replaced with a more convenient representation, so, as you said, the seek time will be reduced.