The Battle of 5 Armies (er...editions)!

[3d6+15]

Until the GSL is released, I can't comment on the legality, but I suspect that the "time and effort" is pretty small, spread among the more avid FantasyGrounds players.

Without a doubt there will be a 4E "ruleset" for Fantasy Grounds within a few weeks of it's release. There are already tons of user created rulesets for other games.

As for the legality and the GSL, that's simply going to dictate whether or not SmiteWorks makes a 4E ruleset of their own.