Well enemies damaging each other can be implemented with a modified turtle armor set codeI've coded some things myself, but no I haven't. I love the idea, it just seems quite complicated.
Wars can be invasions, and with some logistic coding it is possible to make only one invasion, but with different enemies each time.
Spread bonus can work the exact same way the broken demon altars give a spread boost.
So the only thing to code from scratch would be the factions system, but I don't like it as much.