This is actually a real post netting itself amidst the vast expanse of loser April Fool's jokes the internet (and gaming community, more specifically) will be throwing at us for the next day or so.
From www.l4d.com:

To support the SDK, we are extending the matchmaking system to allow for third party campaigns. We will be adding extra features so players will be able to find dedicated servers running the campaigns they have installed. They will also be able to see friends playing third party campaigns, and be directed to download them as necessary. Another major feature we are planning to add to the matchmaking system at a future date is team-based Versus matching. This will allow two teams of four to locate each other and
compete in a Versus match.

On top of this, the latest update for PC allows users to "choose between starting a game on an Official server or the Best Available", a very welcome update to those of us living this far away from most of the Official Servers.

You can check the rest of the blog here.