A simple idea that I don't believe hasn't been suggested before, and one I'm sure I've thought of suggesting before also.
The idea is for the option to be able to hide a troop that you have researched in the respective building you'd produce it in. For example a Roman off player will have the Legionnaire, it's base troop unlocked by default but as an off player you are likely to only ever be interested in building Imperian, so the option to hide this would nullify any chance of the infuriating problem everyone has had of been half asleep and building the wrong troop type. Similar situation with Roman horses, you may want to whilst playing roman off start out by building some EI to enable you to raid, but then switch to EC for the extra attack power once you have a sufficient raiding income. Such a feature would also reduce the reliable on scrolling down when browsing on small tablets/smartphones.
I envisage the best way to implement such a feature would be some sort of + and - around the name of the troop type to expand and hide each troop type, but welcome suggestions on implementation of such a feature