I'm not sure if a ship specific ban is possible even.
Overall I see problems with this though, first off, you could for example die to NPCs, accidents (especially) lanes or other things that don't involve a real fight on any ship, as was mentioned before. Second, what if you wish to train in Conn with the ship in question? You can't expect everyone to only do one fight every few hours or even every half day. And third, people who got enough money could just buy several transports, gunboats or even cruisers and battleships. While, yes, that would be a massive money sink, I feel like it is not how it should be.
The idea has some flaws, also some good sides though. Having the destruction of a bigger ship mean something (btw, keep in mind, a transport is easier to build than a GB...) would certainly be interesting, but it would also cause problems. If caps were made quite a bit more sturdy so that they didn't die in a few second in a fleet engagement...who know. (I'd for example make the weapons have a little dispersion while giving them longer range or such...)
So, meh...in the end I think if the idea were ever to be considered it'd need some refining.