The US Army is aiming to replace VBS2 by FY 2014. That is if they secure funds for it (given the future cuts in defense, who knows). Please see the full article at the Training and Simulation Journal.
“In our gaming strategy, we don’t want to be married to one application forever,” Parks said. “We want to utilize it as long as it’s relevant and it meets our training needs. But we know that technology and our training requirements change from year to year, and we want to remain relevant to our users.”