Arma 3 alpha offered 3 arma3 lite invitations, esentially it was nerfed copies you could give to friends so they could play the game _with_ you. (SP was disabled etc) For "special" games, its a great way to get people into the game, that otherwise would newer have bought it. From my 3 Arma lite invites, i made 2 people buy the game. The "lite" versions only worked for a set period of time. Esesentially an MP demo i supose..
This is a nifty idea, but should be low priority. Would be a nice addition down the line, but after the game is finished and polished.
I'd love this as a "down the line" feature like brian said. It would be quite useful for showing friends the game and letting them get a feel for it before buying.