Would've been nice to seem them meet a few more races that we're familiar with. Any preferences? Edited to add: I forgot Betazoids and don't know how to edit the poll. (*facepalm*)
The Kanamit from the Twilight Zone episode "To Serve Man". I had enough trouble with the Ferengi and Borg showing up 200 years earlier than we were previously told. So there aren't any races from the 24th century I would have wanted to see. Maybe those little gold guys seen in the reception room during TOS: Journey to Babel. But I wouldn't want to see any TOS aliens before their established first contact.
Deltans. Some people seem to think that they are oversexed nymphos, while I love the way they are portrayed in some of the novels, especially by Christopher Bennett in his Watching The Clock. They are sexual creatures, but on more then a simple carnal level. There is a deep, spiritual meaning to their sexuallity, and I'm wondering if American tv could handle sex being talked about in an adult way, instead of the standard HBO norm.
Out of the list, I'd pick the Bolians but I would have liked to see the Enterprise run into the Tamarians and they (or Hoshi) fail(s) horribly. No Darmok and jalad though.
I don't even know who half the choices are. But Cardassian first contact is a no-brainer, even if some fans will refuse to accept it because we never saw them in the TOS era. In fact, they're all no-brainers. It may stretch credibility that all those aliens were met by the first Starship Enterprise, but a prequel series is meant for prequel stories.
Cardassians are certainly possible, since at least one was in the area in the mid-22nd century: Iloja of Prim, on Vulcan. Though, granted, he was an exile. It would have been neat to see Tobin Dax on screen, too.
For reference, the Fed President in ST VI was an Efrosian, the Fed Prez in "Homefront" and "Paradise Lost" was a Grazerite, and Dr. Sevrin from "The Way to Eden" was from Tiburon (we also saw a native of this planet in the DS9 episode "The Ship" and the planet was mention in passing in "Affliction"). I too thought the Cardassians showed promise. It might be interesting if things started off well and maybe have a seen where some friendly Cardassian officer shows off their star charts. Archer inquires about one planet on the edge of the map, to which the Cardassian responds "Oh, that's Bajor. The natives are a primitive, superstitious people. They've never been of much interest to us." The Trill might be promising as well. Since DS9 basically ignored almost all the premises TNG established about them (i.e. lumpy foreheads, parasitic relationships instead of symbiotic ones, joining is a secret etc.), I don't think "Enterprise" would be bound to them either. And yes, it would be nice to see Tobin, especially if they tried to stay close to Colm Meaney's performance in "Facets". Heck we could even meet an elderly Lela, who's fatally injured in some accident during the episode and passes the symbiont to her chosen heir Tobin, a nervous mathematician unsure of himself, but who finds the strength to join.
Weren't there already plans and spaceship concept art developed for the Kzinti for season 5 before the show was cancelled?
^ Yep. They had an episode called "Kilkenny Cats" ready to be written, but I don't think it ever made it out of the concept stage. Linky
I grew up assuming TAS was non-canon, so I'm VERY dubious about bringing anything from it into the live action series.
From comments I've read over the years, "Kilkenny Cats" was pretty much a recycling of DS9's "The Abandoned", with a baby Kzinti being found and raised by the NX-01 crew. They've been referencing TAS since DS9, throughout ENT and even in TOS-R. ST'09 remade entire scenes from "Yesteryear", including Sarek's entire speech to young Spock about the path of logic (which was told to young Spock by the older Spock in the altered "Yesteryear" timeline, reciting what Sarek told him when he was that age) The Kzinti backstory (lifted straight from Niven's Known Space universe) would have needed some tweaking to fit into the modern Trek timeline, though. And that's even if they could have reached an agreement with whoever owns the Kzinti (due to this, the Kzin have been renamed M'dok, Mirak and Kythari in licenced Trek novels, videogames and short stories over the years)
If ENT Season 5 had Kzinti, then it would have ben a great opportunity to create a canon version of the Kzinti and throw out the gigantic impossibility of a "200 years ago" Earth-Kzin War.
First of all, frankly, the idea of the NX-01 crew adopting a baby Kzinti sounds pretty lame. Second, the references have been a bit more subtle than, say, someone saying "hey, remember the time the Enterprise crew met Satan and he was actually a goodguy?" Third, as you said, there's a whole legal mess to work out to reintroduce a race from one animated episode (and yes it's almost impossible to reconcile that whole "Earth-Kzinti Wars" stuff with canon history). Fourth, depicting two-meter tall, furry cat-like creatures would most likely not come off well, given the time and money constraints of a TV series.
I'm not sure I'd use Bolians. I think it was implied that they were quite far from Earth compared to most Federation worlds. Maybe not.