While we're on the subject of lost eras, and moving beyond
The Lost Era proper, I'll repeat what I posted last time the "which unseen stories should be told?" question arose:
I want a definitive Xindi story, or even better a Xindi series (I know, it'll never happen).
I very much enjoyed the Xindi. Although my opinion of Season Three of
Enterprise is mixed, I did like the internal dynamics of the Xindi Council and its member races. There's still a lot of potential there, I think, especially seeing as they supposedly wind up in the UFP (
The Sky's The Limit supports this with a cameo Xindi character in the Federation government). Their internal politics would make for quite a gripping story arc in Trek lit (plenty of ambiguity, interesting aliens, lots of potential for political intrigue, drama, new areas of space to be fleshed out, action - I'm sure they could make it appeal to everyone in one way or another).
I really liked the presentation of a multi-species organization that is always
this close to falling apart and which is essentially a five-way racial feud sitting around pretending to be an alliance, yet which is
trying. Despite everything, they seemed to have a genuine sense of loyalty to one another, to the idea of Xindi as a collection of races, and they were trying to make it work, even if they couldn't actually stand each other. It always looked hopeless, yet they were still there, all five of them. There's something very moving and noble in that, really, and I'd love a more detailed look at it. What keeps them so motivated, what makes them work, each alone and as a whole? And the ability to explore not only five alien races (most of them quite non-human) and a sixth, combined culture built by all these different races in tandem would be exciting. It's world-buildning heaven, no?
I really want to read about the Xindi's "lost era". They're in
Enterprise, and then (so far) nothing until they show up in "The Sky's the Limit", seemingly as members of the Federation (and the Xindi character there was Reptilian; best of all). What happened in between? Did they fall apart, fight among themselves, get back together and rebuild their alliance? What happened to their advanced technology - holograms and vortices, etc? How did Earth react when the Xindi popped up again at a later date and offered a hand in friendship (assuming that's how it happened)? How did the Xindi populace react to the "turns out Humans aren't the enemy but Guardians are, how about that?" revelations?
And the worldbuilding potential! I have a lot of questions about Xindi, which the authors among us are duty-bound to answer

: Why didn't the avians survive, particularly when the Council Chamber on New Xindus/Council Planet suggests that they apparently make it off Xindus after all? Were the Reptilian warriors all male like Dolim, or were at least half female (these are reptiles after all, who can tell what sex they are)? How does an Aquatic "dynasty" work? What does the name "Xindi"
mean - how did they decide that was their collective name, and seeing as it doesn't sound Aquatic or Insectoid, is it a sign of Primate or Reptilian ethnocenticism (they both seemed quite racist much of the time (the Arboreals less so, but then they were more reserved))?
So what we need, friends, is
Xindi: The Lost Era, a short series picking up where we left them and bringing them through to Federation membership.