In regard to 7's, it's my opinion that it's a massive growth area for rugby union and has massive potential..
One area in particularly is women's rugby, women's XV's rugby participation figures have been stagnated for years, now you have 7's rugby and the growth figures are quite incredible.. Obviously growing from a small base, but still growth nonetheless. There are semi-professional female athletes representing Australia at 7's these days with other sports like touch-football and league admitting they are losing some of their top players to union.
Australia are favourites to take home a medal at the next summer Olympics.. This and a home commonwealth games in 2018 will build a lot of momentum for women's 7's within Australia.
Men's 7's are a separate issue, as rightfully pointed out the absence of the top athletes will prevent mass market appeal.. If there were a means to overcome this issue then we might see 7's rugby takeoff, until that point it's going to serve second fiddle to XV's rugby.