I was just talking with some fleet mates about how cool our tier 4 ships were during leveling. Personally I really adore my discovery class ship. To me it's the coolest in the game. It's awesome in looks, great for roleplaying and just keeps reminding me of all those hours I spent watching Voyager episodes.
In short, I was really delighted I could play with this ship when I got to the captain rank.
Now however I'm a Rear Admiral for months. In the beginning I tried flying with the tier 4 ship, however I had to give up on it since the tier 5 was just that much better with the extra BO slots and consoles...
So... Now I'm a sad little panda that choses survivability tier 5 over the awesomeness of the tier 4 ship.
Then a fleet mate just there had this awesome idea I'm totally for! What if we get the option for like a million EC or something to upgrade our tier 4 into the stats of a tier 5?
My fleet mates idea was to have the option to upgrade each tier ship to 1 tier higher. Which I think would also be really awesome, but I don't want to push my luck either.

Advantages:
- More diversity in end-game flying ships
- Happy people, flowers raining down and golden rays of sunlight making our days look brighter
- money sink
- People get to play with the ships they love so much from the shows
Disadvantages:
- None really. The only disadvantage I can think of is that some people might be confused at the start when pvping, but nothing dramatically serious they can't get over.

I have to admit I didn't try really hard of thinking up any disadvantages since I want to fly viably in my tier 4 again, but overal I think there aren't any real disadvantages to it.
Comments
Its really a shame that lower tears are dropped for higher tiers. They are fine ships.
- BO slot upgrade
- extra weapon slot
- etc, etc
You sir, are my hero of the day.