Not challenge - opportunity. These characters don't now, and never have had any interaction with each other. Sulu and Chekov sat next to each other for years of TOS and several movies and have never actually interacted except for exchanging a glance or two. I doubt they've even SPOKEN to each other - only to Kirk and Spock, and FAR less with McCoy, Scott, Uhura. And even then their interactions were overwhelmingly, yessir, nossir, and oh-my-god-what-is-that-thing or I-don't-understand-can-a-major-character-explain-it-for-the-audience-instead.
It can be excused during TOS because, that's just how TV worked (& often still works). The movies did little more for them than the series did, if anything. But clearly the original characters and setting have MUCH more to offer that has gone unexplored onscreen. Uhura has a relationship with Spock? Okay, so it's not the relationship with Kirk that everyone was expecting but at least UHURA now has an actual relationship - yes?
THAT'S the sort of thing that comes of a reboot and I want more of it. Temporal mechanics and logical command hierarchy be damned. Full warp speed ahead I say.