This is "Future ideas", so how about go a step further?
Be able to change the ship roles after the ship is built. The Medium Capital ship is no longer a capital ship after I have researched Huge Hulls (or, more accurately, Epiphanied Huge Hulls--I have yet to research Massive Scale Construction straight up).
I also keep getting burned by the ship role defaulting to Support. I will design & build some behemoth, 1400bc to build--and forget to change the ship role. I wind up with a "support" capital ship that's useless in a fleet. I have to redesign it, and pay a boatload to upgrade the ship I already built (and screwed up).