Okay, I'm just going to throw this idea out there, and I'm doing it on this thread because I don't want too many spoilers. Of course at this point I've already seen the episodes that introduced Kagami and Luka, but I'm already aware that in subsequent episodes those characters are going to become sort of a romantic attraction (or DIStraction) for Adrien and Marinette, respectively. And of course, it's sort of a delaying tactic to keep the wheels of drama spinning; our two heroes can't get together romantically so easily.
But it occurred to me that it would actually be a lot more interesting and believeable if their alter egos were each their own romantic rivals. In other words, since it's already been shown that Ladybug is growing closer to Cat Noir and Adrien is growing closer to Marinette, what if their conflicting romantic feelings were a direct result of their NOT knowing each other's secret?
I bring this up because "Reverser" has, I think a little clue about how their real identities are protected by the very magical transformation that gives them their costumes. The costumes aren't like real clothes and they can't be removed (except in the very special circumstance in "Reverser"), except when their Miraculous normally times out and transforms them back to Adrien and Marinette. Their transformed identities literally become their TRUE selves.
That, to me, indicates that their secret identities are being protected by the magic of the Miraculous -- when they are in their superhero identities, they are being protected from being recognized (BY MAGIC) from anyone else, including other Miraculous users. It's the very same magic that is in effect that prevents their costumes from being removed like any normal clothing. There are other ways that their identities could be discovered, but not just by looking at their physical appearances (or listening to their voices) in their transformed state and comparing them to their normal selves. In the case of Alya/Rena Rouge it's different, because Marinette/Ladybug knows what's going to happen beforehand to her when she gives Alya the Miraculous. She just couldn't discover her regular identity for the first time after Alya had been transformed into Rena Rouge. And presumably, if they're actually SEEN transforming, then the secret is out.
So if Adrien is attracted to Marinette AND Ladybug, and Marinette is attracted to Adrien AND Cat Noir, it doesn't mean they'd automatically put 2+2 together and realize that the attraction was a result of them being, in fact, the very same person. They also act a little differently, and speak a little differently, in their hero personas and that helps reinforce the magic preventing their being recognized. And the conflict would come from their being confused about "Wait... I can't be in love with two different people! Which of them is my TRUE love?" (Yeah, I know it's never been a deal-breaker for Archie, but this show is different.) And THAT would make for some interesting scenes in the episodes.