Was Mekt Gay?: Well, we regarded him as such, or at least he had a boyfriend in the "Reunion" story. But there were no particular plans to bring Mekt into the main storyline. We regarded him as pretty much at peace and happy with his life on Winath -- a resolved storyline. But yes, it would have been fun to do more with him, especially reuniting him with old LSV teammates Ron Karr and Sussa.
How did the Dominators capture all those heroes and quasi-heroes they were experimenting on?: Well, again, no special story, other than that the Dominion had infiltrated Earthgov, which was getting more and more sinister and authoritarian. So the Dominators essentially did it through Earthgov. (Again, the Sourcebook has a few details about how these things were done.)
We didn't have a lot of specific plans for most of those characters. They really came about just because there were panels during the Terra Mosaic where we had to write up lists of people in the chambers and we thought it would be more fun to come up with people who tied into the Legion universe than just random names. I guess over time, we'd have had some fun with a few of them, but I think we generally just regarded them as background characters. (It's worth noting that we were always under pressure to focus on the core Legionnaires, so there wasn't much chance these lesser characters would ever get much spotlight.)(It's worth further noting that there was never much chance that we'd have a real say about any of these matters. Basically, as soon as Keith left, we were just playing out our contracts and there was no real intention of keeping us beyond that. We certainly had ideas and suggestions, but I don't think anyone was really listening. The one exception is that our last couple of editors were really trying to help us come up with ideas and stories that would create the kind of commercial success that might allow us to prolong our stay, and if we'd somehow turned Legion or Legionnaires into real top-sellers, we'd have probably had a lot more support than we did.)
Amethyst/Mysa: Yes, we'd probably have brought her back as a regular Legionnaire or at least an ongoing supporting cast member, as the merged version of Mysa and Amethyst. It would have been nice to show the long-suffering Mysa finding strength and fulfillment through her union with Amethyst.
Martian Manhunter: Our notion was the MM simply had survived into the 30th century and was a known and respected "elder statesman" of that era. In our minds, Mysa had an ongoing affair with him, but the MM editors didn't want anything in print to establish that, since, for one thing, they'd be biologically incompatible. We still liked the notion of him as one of the many formidable males Nura was *ahem* quite familiar with.
Dragonmage's Origin: We had a pretty involved back story for him, but he's basically just a very talented mystic, born with so much power that the problem was never not having enough power but always having too much and trying to harness it. We probably won't discuss too much of his back story, since there's no reason now that we can't use it on some other original character (and, in fact, Dragonmage was pretty strongly based on a couple characters we'd created earlier for fan fiction projects).
Catspaw's Origin: Catspaw was actually created by Jason Pearson. At one point he and we were trying to work out a "Legionnaires" fill-in that would have given more of her background, but we didn't start thinking about that possibility until our time there was almost up. Basically, Catspaw was just a woman on Earth when the Dominators were secretly nabbing people and experimenting on them. There was a boyfriend character (from the Legionnaires story where they meet all the Protys on Antares, I think his name was Ansis) who was supposed to have somehow betrayed her and been the cause of her being kidnapped by Earthgov/Dominators.