The fans I knew growing up preferred TNG but I and others were much more TOS. Most people I talk to in the day to day think of TOS when talking Star Trek. Even my mom, who hates science fiction.
As for new fans, I think new fans will come in as they find something of interest to them, be it SF, or characters, or action or comedy. Whether or not they'll stick around comes down to how they feel like they can interact with the community.
For me it's an age thing. Those who grew up with TOS (ie. before TNG existed) prefer TOS. Those who grew up with TNG (ie. started ST with TNG), don't like TOS. The only reason I bring this up because, aside from new fans (post 2009), these are the 2 biggest pools of fans, and may be indicative of new fans today.
TOS is clearly the winner in terms of pop culture. Everybody (above 30) knows who Captain Kirk is and "Beam me up Scotty", even if they never watched the show.
I guess I'm trying to answer this:
Will TOS maintain its legendary status as Trek fandom gets younger?
To me this means those who watch a new show, not pop culture.
Hence for new fans to connect to TOS, they really need to be open to wanting to continue exploring the lore. New fans coming SNW IMO is the best entry point to really connecting with TOS.