It's worth a try just to see how the game would pan out. With an even number of players on each side, there is a man to mark for everyone so why the need for the the offside rule? it is the most contentious issue in the game and causes the most trouble.
I understand that this has been tried by FIFA at younger level tournaments (heard that a couple of years ago in a football debate which discussed offside mistakes by refrees) and this was not conclusive at all as each team would keep a maximum of players in their own half and only a couple attacking in the opponent's half. So attackers were always hugely outnumbered and the game sort of stood still.
For me technology is important in 3 cases only, goal line, offside and penalty box decisions, basically the main match deciders. If that's too much, i would keep the first 2 cases and use the official behind the post for the penalty box decisions.
