I hope Sevens mode is not to easy, and well thought out.
Also Be a pro mode, this could go two ways. Either you control your whole team, but you progress your own player within that team or you play with AI and you control just you. But like AzaMatt said, it would be nice to play the set pieces, so that way you have 'control' whether you win or lose.
Hopefully if its just you, then you can control (once captain) line depth, defensive strategies and attacking pods and attacking lines etc, and have buttons to call for options, such as receive a pass, ask for a kick, etc. This way you can position yourself in the right areas and not just 'hope' it comes to you. There must be player progression in this, other wise people will just overpower their player to be 100 from the get go. It be nice to earn experience and then spend the points. Also it be nice to manage your player not just from game to game. E.g. Play a game, spend points, play another game. Be like Play a game, spend points, talk to your coach, talk to your manager, other players, talk to your agent, receive job offers, receive injuries, receive emails about how 'bad' you are doing and stepping up your game, being promoted from sub to starting 15, changing your position (especially if you choose something that you don't like and have to begin all over again). Thoughts...lots to think of.