battle plans are rather complex things, atleast as i want them, and you would NOT be able to make them in 15 secs. most likely you spend time fidgeting with your plans while not gaming at all.
I remember this very very old Unix game where two player pitted their robots against each other. It worked so, that there was a C-function interface that provided you fucntions to control your robot and functions that returned sensor input data. You then wrote a C-program using that interface and compiled it. When started the two competing robot programs would connect to a server process that fed them sensor data and responded to control calls thus playing out the battle. As the robot "AI" was written in a true programming language you could make it as complex as you wished. The graphics were crude but the game was actually quite fun.
While we could simply publish the ship battle interface for FreeOrion I don't think very many ordinary gamers would like to actually use it. OTOH it would provide a way for those interested in such things to improve on the game AI.
I myself would prefer a somewhat simpler solution, though.
Using the dreaded real world (*gasp*) as an example I'm now going to step on the toes of all the control freaks here:
FreeOrion will have computer opponents. That much is clear. However, from this it follows that the computer AI will be adequate to competently control a fleet of ships against the player. If it were not so then there would not be much point in the game. The computer opponent must be good enough or people will not play the game. But if the AI can fight reasonably well against the human player then it also by the same logic could fight reasonably well _for_ the human player as well.
In the real world an admiral does not directly control every single ship in his fleet. He plans mission objectives, prioritizes tasks for different ships, and gives general commands usually even appending the clause "as the opportunity arises", and then relies on the ship captains to be reasonably competent to act on their own. In fact it is a generally accepted military doctrine that the commanding general should not interfere with how his field commanders do the job as long as they do it, because usually the field commander knows the actual _local_ situation the best. The job of the general is to manage the battle as a whole and if he directly overrides his field commander then he better be darned sure he knows what he's doing.
Couldn't we do something similar in FreeOrion, too?
You would decide on a mission objective for the fleet engagement, like "Attack that planet", "Defend this planet", "Destroy enemy fleet", etc. You'd also set how hard you want the mission accomplished by setting triggers as to when to retreat like "50% of fleet destroyed" or "Less than 10 mission critical ships left", etc.
Then you would assign priorities for your individual ships or ship groups like giving some the command "protect mission ships at all costs" creating your point defense force. Some ships would "actively seek out enemy positions" so others can target them and some would "engage enemy at will" perhaps with extra target priority lists designed for your capital ships so your missile volleys go after the enemy capital ships first. Or however you want them.
You could also set the initiative level of ships, i.e. what to do when "opportunity arises". Like would your point defense ship hold its missiles and guns ready for a possible future incoming volley (= low initiative) or would it shoot at a enemy ship if it comes inside the range (= high initiative)?
Of course, the priority and target lists for the individual ships and ship groups could be made well in advance as a form of "standing orders".
After the commands are issued you hit "Go" and the die is cast. The actual battle will then be in the able hands of your ship captains except you could give some general battle directives, e.g. "retreat".
I would definitely not want to control each and every ship in a 100+ fleet even if it were in the MOO2 turn based style with unlimited time. However I would very much like to _see_ that 100+ ship fleet in action fighting that epic battle against the 100+ ship Klackon mother fleet. With multiplayer even more so. If the battle is mostly automated it could even be played "behind the screens" in situations where real world time is an issue (like in multiplayer) or you could play it out in double or triple speed.
IOW to quote the famous words: "Trust the computer. The computer is your friend."