As I see it, a lot of people already stuff the bug number into the summary and I can't really say anything against that. It gives a nice overview when you look at it: https://gitweb.gentoo.org/repo/gentoo.git/log/
Given that fact, I am not sure we can convince people to repeat the bug number in the description of the commit. However, the bug url definitely does not fit into the summary, but in the description. That would be an argument for the bug url thing (so we actually have both). As in: try to stuff the bug number in the summary and also give a link in the commit description in the form of "Gentoo-Bug-url: ...".
