It probably wouldn't be too difficult for FFG to design unique armadas, but to print all the unique sets creates a whole lot of shelf space.
Then there's the problem of distribution. I don't think many game shops would have them in stock locally. There're just too many types and too little owners of the game. There're quite many players, and I'm happy to get more every other month, but essentially, one game can last for a dozen and more different players. FFG probably has better numbers to judge if such an ordeal would make sense.
I'd be interested in a few armada-boxes for the races, though of course it'd be nigh improbable to get them all in one go, financially.
That'll probably be again the cost of the whole game on top.
I highly doubt it would make sense to include race-specific armadas in a new edition of TI. The sheer of amount of plastic, the weight of the box, would be devastating.
Then, we have the issue of 3D-printers. FFG takes the effort to design the things, box them and put them on the shelves, but… then people will say "Nah, that's too expensive for me, I'll rather download some mesh and print it myself."
Looking at it from this angle, the "easiest" way for players would generally be to design armadas themselves and print them themselves.
It's hard to forbid you doing it anyway. You could play TI with Warhammer-Orcs instead of ships after all *cough*
Oh, and did you think of the ADDITIONAL SPACE the game will take up in your home? Or how even more hard it will be to transport to play at a friend's place? Remember you probably won't be using more than half of the special armadas per game anyway.
In any case: I would definitely want to paint the ships myself. - But then there're people who'd rather have pre-painted bits.
Not everyone knows or has a loving painter in their groups.
And I would really like to hear FFG's opinion on this whole topic