I still have the feeling that Admiral-level gameplay is one of those design areas that's going to wind up getting short shrift when implementation time hits.
For one thing, it seems to be incredibly rare in the MMORPG development world to find a developer who is capable of designing (or perhaps "who is allowed to design" would be more accurate) gameplay that's more abstract than concrete. It appears to be vastly easier to crank out 3D objects -- and ways to destroy them with pretty particle effects -- than to imagine new systems that don't have "physical" components in the gameworld.
Which means that Star Trek Online's developer is likely to have a hard time from the very start coming up with strategic gameplay content, since that's harder to conceive than content that's about directly and visibly interacting with concrete objects.
For another thing, there's the problem that development time is a very limited resource. If the developers agree with my guess that most gamers want tactical-level gameplay, which means object-based, direct-action-oriented content, then it's likely that they're going to focus on creating that kind of hands-on, immediate-action content as the bread and butter of their game.
Since everybody always underestimates how long it'll actually take to implement a design, and since any MMORPG developer is likely (I'm not saying "guaranteed," just "likely") to consider tactical-level gameplay more financially important than strategic-level gameplay, it's possible that very little time and attention will be given to the Admiral game.
If that's the case, then having multiple Admiral ranks is a problem, since there wouldn't be enough content to keep all of them busy.
Finally, it might be worth noting that no developer ever expects any player to max out their level as fast as some players will always actually do. If the folks making Star Trek Online follow suit, it's possible that they might think along these lines: "Well, nobody's going to reach Admiral the first two or three months after we launch -- that gives us time to add the other Admiral-rank content as a patch after we launch." (Unfortunately, that assumes there won't be other post-launch issues discovered that require developer attention -- rarely a good assumption.)
So overall, it would not surprise me to see Star Trek Online launch with just a single "Admiral" rank, mostly to allow the developers to develop and polish the lower-rank content that more players to start off with are going to be more interested in.
All that said, I wouldn't mind being proven wrong on any of this. I'd love to see Star Trek Online designed and developed to launch with so much strategic-level gameplay that not only does it need multiple Admiral ranks, the admirals also need Commanders and Captains to serve in adjutant and XO roles. That sounds like it could be a really fun game.
I'm just not betting that ST:O will go that way.
But don't let me stop people from speculating on how a multi-Admiral system might work!