Equally splitting large fleet by selecting ships one by one is a long and boring pain in the ass (and in multiplayer with no pause button, even dangerous) . Its one of the reasons all players eventually end up with single large fleet, and strategic aspect becomes uninteresting. I propose an automatic fleet split button, which would split all corvettes, frigates and cruisers in a large fleet equally into smaller fleets. Capital ships and Titan could still be assigned manually after the split, but smaller ships need this (especially with normal and large fleet sizes).
Its one of the things that would be very easy to do (I think), and would greatly enhance the gameplay.