I have been playing skirmishes quite often since the second beta trying to hone playstyles and fleet compositions. There is one thing that I would like to be able to do in Skirmish however, that I cannot do:
Design fleet compositions to counter other compositions.
I recognize that this may be a feature that may need to be added post-launch at this point, however, it is a feature that I feel would make testing strategies and factional balance easier. For example, there is a meta posted lately complaining that carrier meta is the only meta. However the only way to test counters to this is to play against other players in multiplayer who are running said meta. It would be significantly easier to design an AI Imperial Fleet stocked with carrier-ish ships and test your strategies on that.
This said, it would be a lot more of a Quality of Life feature than a necessary feature. I hope that it may be added.