I'm a millenial myself (36 years old next year... I'm getting too old for this), and while I can think of some "popular" names of my generation like Linkin Park, Dragonforce, Emma Watson, Brittney Spears as you mentioned, Mario, Pokemon, World of Warcraft, Indiana Jones, Harry Potter, The Simpsons, Futurama, and so on, none of them can compare to ye olde icons of ye olde generations like Star Trek and the people I mentioned before.

Celebrities and pop culture sensations of olden times defined entire eras that we can still clearly identify to this day, but that just doesn't happen anymore because large numbers of people aren't forced to coalesce around a small handful of works and figures.

>we can have social cohesion without resorting to nationalism nor religion.

Can we? The way I see it, in removing and villifying tradition, religion, and nationalism/patriotism they were simply replaced by inferior substitutes and surrogates. The chief examples being "science" ("Trust the Science.") and politics (Obama, Trump, Farage, et al.) as the receptacles of peoples' desires to be fervent about something.

>none of them can compare to ye olde icons of ye olde generations like Star Trek and the people I mentioned before.

Well a lot of that comes with time. None of the people nor ips you describe are more than 30 years old. Star Trek is over 50 years old. We don't know which are gonna last 20-30 more years. Pokemon is going strong, but HP has been dipping for a while, and The Simpsons is well past its prime.

I think it's also simply because we are more globalized. Is Pokemon and Harry potter bigger than Star Trek ever was? Absolutely. But it's also easier than ever to globally broadcast anything anywhere, especially when offering localization for more access. I don't see this as a bad thing.

>Can we? The way I see it, in removing and villifying tradition, religion, and nationalism/patriotism they were simply replaced by inferior substitutes and surrogates.

Sure. The world is larger and brands bigger than ever. But when things globalize, that creates a need for smaller, more local community values. Bringing back third places would help more than trying to make the next Star Trek.

Now, will people be receptive to such activity? I don't know. It's not up to me to figure out what people like or want. But those places being defunct answers the question for us without even trying. And I wager there's more than enough community to create out of those that do.