Malx: My local mod_virgule lets you give diary entries a topic. If this topic matches a project name, the entry gets added to the project page in recentlog style. I'm biased of course, but I think this is a much nicer way of getting the functionality you want than the way you suggested.
My patch isn't completely ready yet though, which is why I haven't submitted it to virgule-dev yet. The biggest problem is how to let people specify the topic unobtrusively. For now it is a seperate text entry on the diary entry form, but this means you get only one topic per diary entry. But people seem to be aggregating several topics in one entry (which is very understandable, since you only get one entry in the recentlog).