I'm probably completely off base because I've only been around for one project, but I feel like a lot of people that are initially drawn to the concept of a Create-A-Pokemon forum are turned off by the rigidity of the process. Or they might not be so much interested in the competitive aspect and might just be interested in the flavor aspect, which I do think deserves to be better catered to on some level (I've only been here for 1 project, and I already saw way too many "who cares about the Pokedex entry anyway?" comments). Perhaps allowing a more casual air, allowing personal projects and topics that have little or even nothing to do with the main CAP projects themselves, might draw more people to the CAP projects.
For example, there are a lot of submitted concepts that never get expanded upon. What if they were allowed to be discussed and worked on in their own threads? Maybe somebody was super intrigued by Fire Blast's Theoretical Threat and decided to see if they could tackle the concept on their own. Or maybe somebody had an alternate concept for Sketch Artist that they wanted to show off. These things wouldn't make it into the CAP metagame, of course, but they could be fun to throw around just to have hypothetical discussions that could benefit the CAP process as a whole by generating interest. They could even be a vehicle for finding posters willing to put in a lot of work for CAP, posters that just don't feel like the current air is welcoming.
Between CAP projects, concepts normally reserved for concept submissions could have their own threads where they could be discussed and speculation over. This could be a way to determine interest in certain concepts and even to do some preliminary work to discuss the many ways that a concept could be done were it to be selected.
This could also allow people to discuss things that CAP usually isn't willing to discuss, like Pokemon made for double battles or the UU metagame or new evolutions for existing Pokemon. Having an outlet for those desires may make people feel more like their personal desires and needs are being met even if not by the larger CAP process.
Or people could try seeing what would happen if CAP were done from different angles. "Here's the artwork that was chosen for Necturna, but what stats, moves, abilities, etc. would you give a Pokemon that looked like this if you had no idea what this CAP's purpose was?" Or other hypothetical games like that.
Who knows? Maybe if some of these smaller personal projects gain a lot of traction, they could be deserving of promotion themselves into fully backed projects.
A lot of this I doubt will happen, and I could be totally wrong about it being able to offer something to the CAP project, but you asked for thoughts, so I thought I'd throw some stuff out there to see what if anything sticks. I didn't expect my post to be as long as it turned out.
I don't know, a lot of what I've thrown out only really addresses the first two point and may not actually benefit CAP projects themselves. It certainly has the potential to get out of hand and eclipse the CAP project if not kept in check, but I do think that there could be ways to make the board more casual like this, allowing people to do their own thing outside of the official CAP project some times. I'm glad that it's being discussed either way.
One thing that I don't think will help at all, though it was a valiant effort, was the "Flying in the new CAP Metagame" thread or anything along those lines. I was excited to see something on the board that wasn't a process thread, but I was really disappointed at how technical the topic actually turned out to be. That's fine for people who are really into the competitive metagame, but for people like me who are more casual and who aren't necessarily drawn to CAP for its competitive side (and I don't think that I'm the only one), threads like that are exactly the part of CAP that we just don't care about.
I get that CAP is guided by a competitive goal, but I don't think that means flavor and/or art discussions should be thought less of the way that they sometimes seem to be. That's exactly what I think turns off some of the more casual contributors... I also get that Smogon in general is a competitive site, but I don't think that the only people who come here are competitive battlers. I personally come because I'm very interested in competitive battling, but being interested in and being good enough at to discuss are two entirely separate things. Think like people who like watching sports but don't really have any desire to play, the fans. "Athletes" aren't the only people who come here; the fans do too.
Here's an idea. The prevos were introduced as a fun way of doing more flavorful things to the CAPs, right? Well, maybe we could take it a step further and do something more on the artistic or creative side? Maybe now that Necturna is finished, there could be a competition to see who can write the best story for her, something deeper please than the pokedex entries, like a comic strip or the plot for an episode or something like that. I feel like ignoring these sorts of more flavorful aspects is part of what turns some people away.
tl;dr - Figure out some way to let people try to explore their own ideas rather than being entirely restricted to the main CAP project, or Figure out some way to expand upon CAP's more flavorful aspects rather than only its mechanical aspects.