Tradelanes are actually pretty huge. you can probably tip a rheinland turtle head down vertically - and it would not interfere with any transit in the opposing lane. So, i do not think there is much in the way for aesthetic or mechanic reasons.
The problem really is mainly the steering through rocks - or navigation near celestial bodies. a minor problem might be certain stations that have their capital ship docking points located in an area that obstucts very tall ships - so that the ship would get into an endless loop trying to dock, but inevitably colliding with the station upon lining up.
In terms of balance i daresay a very short but tall ship is harder to hit than a very flat but long ship due to the ships movement. So it might not be easy to balance it. But nevertheless - different shapes are always exciting - kinda too bad we already had plenty of threads explaining "how we do not need new ships..." ( kinda why you don t really get new ones anymore )