Just wanted to point this out:
http://www.dynebolic.org/
Though it doesn't fit the size criteria.
Also: Debian+kxstudio repos works perfectly here. You can start with a mini.iso and add
up. Of course, it won't be perfect. Nothing ever is.
I do agree, however, with your thoughts on lightweightness. It'd be nice to have an
audio distro whose goals include being as light as possible.
But I highly doubt it'd fit in a 30MB iso. Maybe sub-300MB? It could include jackd,
qtractor and some plugins. But that would mean duplicating the effort of avlinux and
kxstudio. Perhaps one could use one such distro as a base, and build a light iso for older
computers?
Does anything alike exist?
Does anybody else feel the necessity?
It can't bother, certainly.