Sometimes I find myself in a situation, when I need to use both
RESTRICT=fetch for the main distfile and allow fetch for additional ones
(langpacks, extensions and so on).
Sometimes it is even impossible to split that additions into separate
package, since they might want to replace some file (for example, Dear
Esther's translations).

So, in that case, I think,  it'd be useful to change SRC_URI behaviour a
bit:

for example:

SRC_URI="
	restrict://dearesther-linux-06082013-bin #fetch restrict
	linguas_ru? ( http://www.dear-esther.com/translations/DE_Russian.rar )
	linguas_hu? ( http://www.dear-esther.com/translations/DE_Hungarian.rar )
        linguas_hu2? (
http://www.dear-esther.com/translations/DE_Hungarian2.rar )
"
Alternatively it can be even:

SRC_URI="
	restrict+http://foo.bar/moo-123.run # mirror-restrict or specifying a
link for fetch-restrict (like for oracle-jdk)
"

And, moreover, I guess, SRC_URI can even be used for VCS:

SRC_URI="
	git+ssh://github.com/lol/moo.git
	hg+ssh://bitbucket.org/lol/moo
	svn+ssh://assembla.com/lol/moo
"

And it can also be extendable:

SRC_URI="
	hg+http://prosody.im/trunk
	modules? ( hg+https://prosody-modules.googlecode.com/hg )
"


Any thoughts?