SL-based platforms aren't a good choice for real-time games. Basically, unless you're running a dedicated sim in SL with very little on it, then lag is going to be a major problem. As much as I love OpenSim, its performance would be even worse.
I've always thought that SL is a better platform for turn-based games. If you think about real-life, apart from sports, most games are turn-based, from hopscotch, to Monopoly, to Warhammer, to poker, to spin-the-bottle. Although this is hardly an epiphany, since most of the games that I've come across in SL were turn-based.
Anyway, since New World Notes reported that SL's new CEO had worked on some Open Source miniature wargame rules, that seemed like a perfect fit. I'll update on progress.