The area will always be limited, unless you own a very flat planet ;)
Few years ago, before I got my vive, I was thinking about using any space available, so if there would be a narrow gap between a wall and a bed, it could be utilised. When I got vive, I realised that it requires rectangular play area anyway and I dropped that idea.
I talked to few devs who were able to test mobile VR devices and one of the problems they encountered is that when moving between rooms, it was getting a bit off. One dev said that they created their office but changed it to be a horror scene. And when they were testing, it sometimes was ok, but sometimes it was off by a few centimeters. I hope that it was a matter of an older prototype device or something random and that when Oculus Quest hits the market, you will be able to wander around the house but always have that 1:1 matching. It actually should be, even if it gets off in couple of places, it should get back on track eventually - it analyses the environment. But yeah, it should be possible, it would require a different level generators that would allow to use different rooms and that would create corridors between these rooms.
That big field sounds awesome :) At some point I was considering adding a multiplayer. And I know that I will want to try doing that. But that's a plan for a rather distant future. One of the things that are important then is to have a separate play areas. Otherwise players may realise that while the world is built using the impossible spaces concept, they, the players, still are bound to our reality in which two objects can't occupy same space.