Regular main page news/announcements on major comp events.
Browser support for streams should be a no-brainer
Definitely improve demoui and build in better support for custom HUDs
Build PREC -like settings into the game for automatic demo recording with configurable settings.
Completely overhaul the QP rules:
Loosen restrictions that were popular in good pub communities: e.g. class limits and some forms of reserve slotting (there are probably more). Or allow people to QP to 'community' servers that meet different criteria than the current QP ruleset.
Add SOAP and MGE servers to the QP options or, better, take those mods into the game itself as betas/modes.
Re-activate the beta client and do testing/balancing of commonly whitelisted items again - focusing on the 6s and HL modes (or whatever they want us to play) - to validate Valve or the community's stances on those items . Hold competitions in these beta modes with prizes to encourage top level play and bring balance adjustments into the game accordingly (ie the Valve's game event but ongoing and official).
Develop new official maps in 5CP, KotH and PL that can work in 6s/HL.