I also had my battery swell recently to the point where the bulging was visible and noticeable as the mbp wouldn't lay flat on the table anymore. When I consulted the apple store (Berlin) about it they told it I need not to worry about it and I wouldn't be eligible for a battery swap as the mbp was performing 'nominally'. I was sceptical and let the battery drain over night, it ended up turning off at ~30% supposed capacity. I brought it to an 'unofficial' repair shop who instantly opened the mbp, the bottom lid was thrown off due to pressure after removing the last screws. The battery was swollen to the point where it looked like it was about to burst and the repairman was visible nervous. He ended up removing the battery on a outdoor table and replaced it.

Something similar happened to one of my colleagues too, albeit after just 3 months of ownership.