I just found out that Portal 1 seems to have been moved to SteamPipe, and therefore received a GNU/Linux port. This means that Aperture Ireland is closer to having a more efficient install mechanism and the Content Porter is closer to having a more viable replacement. Just a small bit of good news!

EDIT (Two days later): I see L4D2 seems to have made the transition now as well. Portal 2 can't be far off so!