Redmine

+1
(mediawiki does that :-)

Yes, I also think this would be a better way to link to Wiki activity.
mediawiki goes one step further and sends the differences in the RSS feed. I don't like that as much (probably because sometimes they collapse 2 or 3 changes in one notification), but a link to the diff page would prevent me from always having to click the History link and the View Differences button to find out which was that single word that changed in a very long page - I'd get that just from clicking the link of the Activity feed.
1 click instead of 3 clicks is always better if you ask me ;)

I really miss easy access to the diffs of Wiki pages, and my preference is to actually have some kind of summary in the feed. We do a lot of small fixes: a bit of improved formatting, a typo fixed, etc. The in-stream diff helps sorting these from the actual content changes.