I think the Seven Years' War would be a very good setting for a game. Due to it nearly being a world war, the game could include units from Great Britain, Prussia, Austria, Spain, Portugal, Sweden, France, Russia and even the Mughal Empire and native Americans. This massive amount of belligerents would allow for a great variety of maps in all the different theaters, from the forests of the Thirteen Colonies to the fields of Europe, from the snowy expanses of Canada to the steppes of Crimea and even the jungles of India or the trade posts in Africa. Take this and add 500-man servers, proper naval combat with working naval artillery and some proper marketing and you have a game that I'd be willing to donate at least €200,- towards.