As I see it, the main issue isn't so much that we have too many different channels for discussion in and of itself, but that not everyone bothers with checking all of them. It was pointed out that aggregating everything would lead to too much noise, but what about aggregating notifications? The forums allow us to subscribe to threads, but that doesn't solve the problem of noticing the threads in the first place; the Planet blog isn't always relevant to everyone, and the Council blogs doesn't post things unless they're important to most people; not everyone likes mailing lists clogging up their inbox.
What I'm suggesting is not a central place for the content itself, but a central way to find out about content. Something that would pull in blog posts, recent forum threads, mailing lists, and filter them according to what the user cares about (this is vague, but a consistent tagging system could work), and merely send a daily digest (or whatever - user-configurable) of headlines to their inbox. Even if it wasn't perfect, IMO scanning a list of links with a few I might not care about is better than having to check 6 different places to find out the same information with even more noise.

Just my two bits - no idea if it's practical or if anyone else agrees, but that's what came to mind when I thought about it.