....
Oh okay, well my comments are still pretty much the same. Instead of introducing more major races, they already have a bunch of existing major races that could use a lot more exploring. You can pick any one of them and do an entire series featuring just Romulans, or just Klingons, the volume of material you could mine would be endless.
To be honest, I don't like the TNG-era Romulans. And the klingons barely. They certainly have potential in capable hands. But through endless repetition they have become totally clichés and walking stereotypes. Everything about the klingons has to do with honour and battle, and every plot involving Romulans is one with deceit and intrigue.
Thats why I love the Cardassians so much: They are a 'newer' race. There is still unexplored potential. They are very militaristic and colonistic. But they can also be clever and intriguing (look at TNGs 'Chain of Commands'). They feel like people.
And that's something I really miss about the Romulans or Klingons, and why I would rather see new recurring species or old ones better fleshed out. Like the Andorians on Enterprise. So come on: Tell me stories about the Bolians. Nausicaaner. Tellarites! There's endless potential, no need to always fall back on the old and tested!