Eh, the whole not taking off your helmet thing is new anyway. I assume it's for their safety and survival following the Imperial purge of Mandalore. In both The Clone Wars and Rebels, it wasn't a thing - your helmet was just what you wore in battle because beskar could withstand blaster fire.
Interestingly enough, Mandalorian culture becoming a religion may well imply that's how it survived. The Empire was pretty damn good at stamping out the Jedi and effectively erasing their history, so it stands to reason they'd be just as good at making the galaxy forget the Mandalorians ever existed as a people.
With the reveal of the Darksaber, knowing what that weapon signifies and its importance to their culture, I'm very confident the show will cover the Mandalorian people coming out of hiding and rallying behind whoever reclaims the Darksaber and becomes Mand'alor.
And it's totally going to be Sabine. 😎