Have a more open line of communication with the community, perhaps a weekly community interaction post or something on reddit/steam/twitter, where we can give feedback and get insight about where the devs see the game going. I know the Valve company line is basically about giving up as little info as possible between updates, so as not to contradict yourselves if things change down the line, but with a game that needs community involvement as much as TF2 does, that policy will end up doing more harm than good. At the end of the day, the average user going to be mad about something or other even if they don't know what's going on behind the scenes, so it's better for the people who do want to have positive involvement to have a way to provide input.
Apart from that, there are a lot of things that seem to basically be prerequisites to playing the game reasonably well, as far as editing config files and changing settings go, so having some of those be defaults, or at least easily accessible through the options menu, would be great. Speaking of the options menu, it would be nice to have the long, scrollable, list of multiplayer options changed into a larger panel with a few tabs, so that everything can be laid out a bit better. As it stands, some options are a pain to get to. It shouldn't be easier for me remember console commands for every option I want to change than to go and hit a toggle in a menu.