Star Trek: Discovery is really going in on past concepts in its final season. The last season is centered around the Next Generation episode "The Race" where we discover that many aliens in the Trek universe share some patronage of some kind from a singular bipedal alien race. It's a lame concept but it's the one they're going with.
In a recent episode for Discovery, "Whistlespeak", the series called back to the rarely-ever seen and very rarely used alien race, the Denobulans. Made famous on Star Trek: Discovery, the Denobulans were a key aspect of that series, as their ship's doctor was Phlox, a Denobulian doctor.
During the show's live, we got to see a lot of Phlox, who had multiple wives, and even more children and was generally seen as a jovial member of the ship. A key figure in the goings-on of the ship episode after episode, Phlox became one of the more dynamic personalities not just on the show but across all of Star Trek.
Yet, despite being a deep, interesting, and unique character, not only did Phlox never appear on any other shows after Enterprise, but we've never seen another Denobulan either. Granted, while Enterprise was a prequel, it was the last show made in that era of Star Trek shows.
So when The Original Series, The Next Generation, Deep Space Nine, and Voyager happened canonically, the race known as the Denobulians was not even created yet. So it's part of the reason why we haven't seen the race of aliens much. While we haven't seen them featured since Enterprise, we do know thanks to Memory Alpha, that the Denobulians appeared in four episodes across three shows since their debut.
Lower Deck's Mugato, Gumato, Prodigy's Asylum, and Crossroads, and Strange New Worlds Tomorrow and Tomorrow and Tomorrow. While used to a varying degree, the shows never truly featured them. It'd be nice to see that change.
With so much chatter around doing something in the Enterprise era of the timeline, and maybe the Kelvin version of that era, it'd be nice to see more Denobulians, as they represent a vastly underutilized portion of the Star Trek mythos that we'd like to see more of.