So Let me start by saying I'm completely against the Admiral rank for players (See my signature). Having every player in the game walking around as an Admiral eventually just seems silly to me.
That said, I'd find it slightly more believable if we were given multiple ships to command!
Think about it: We customize our ship and out Bridge Crew right? Well imagine if we now had multiple ships in a Fleet we controlled, and were able to customize and crew each of them and have them fight with us in battle (rather than just having 8 ships we can switch between and use one at a time, transfering our entire bridge crew with us).
My initial idea would be to give you a second ship you command as soon as you hit Rear Admiral, then add a ship every two levels.
This would add a lot more by way of end game to the game, in my opinion, and actually make the admiral rank mean something for a change. Just imagine the possibilities of having multiple ships to crew up, types to pick, load outs to decide to compliment other ships in the fleet etc.
It would add a lot of possibility, and a lot of time consuming fun (which equals people keeping subscriptions longer and $$ for Cryptic of course).
Until you can assemble those ships together, have them individually crewed, and get to order them around with out being on their bridge, you do not have a Fleet. You have a space dock with 7 empty ships in it.