>What would the game be about?
World Conquest simulator. Each player controls a given area that has resource production, has certain starting military units and has certain opportunities to recruit other military units depending on territories owned, units recruited and nation chosen at the start of the game. Only those units can ever be recruited, thus all metagame is based around this principle. Naturally, there would be different types of units and some may be more effective than the others, but such details would need to be worked out in development.
>What genre would it be?
Turn-Based Strategy. Think Dominions/Sengoku Rance on steroids. There are multiple board games about this type of thing that one can take inspiration from as well.
>What audience would it appeal to?
GS/4X fags. Granted, it would be a lot more simplistic.
>What engine will it use?
In-house engine. Simplistic graphics and so-so netcode would be adequate. One wouldn't need to sync gamestates very frequently anyway.
>What platform (or platforms) will it be released on?
Just PC because support for consoles would be a bitch. Maybe Lunix as well.