I think trying to market to the "casual community" is basically useless because casual players as a whole will never be competitive-type players. RGL tried marketing to casual players with "No Restriction 6s" and to an extent Prolander which were total failures.
6s is its own game and needs to be treated as such; trying to appease people who say "I would play if I could use engineer more" or "I don't like the fact that there's x rule" will never help grow the scene and can only cause the 6s we know to die and get absorbed into the casual sphere. In other words, appealing too much to casual players can only cause 6s to lose its identity and not be 6s anymore. Sure, groups like TF2CC cast a really wide net, but then we get in a situation where (literally) people are asking to get their pubs demo reviewed, etc., and it ends with almost no one sticking around because they're all casual players at heart.
This is why it's important to appeal to competitive-minded people to begin with, rather than just TF2 people in general. Purebred casual players simply play a different game than us. Maybe trying to get people who already play competitive movement FPS games to test out 6v6 TF2, or having some kind of ELO-based matchmaking service that only appeals to competitive-minded players in the first place would work. Part of the problem is that a lot of people in and out of TF2 don't even know "comp" exists to begin with. I don't know how we'd fix that.