OnePlus listed several features as notable when it announced the One in an unnecessarily drawn out fashion earlier this year. One of those items was the selection of StyleSwap covers. The battery in the OnePlus is non-removable, but the back was designed to be replaced with other finishes and materials. However, manufacturing issues have caused the company to cancel the StyleSwap covers completely after a long delay. OnePlus explains on its forums that this isn't settling—no, this is just "complicated decisions."
While producing the first run of bamboo covers, the company noticed the rate of manufacturing defects was unacceptably high. Additionally, the process of swapping covers is somewhat difficult and can lead to battery damage. The covers themselves are also prone to creaking when they've been removed a few times. With this in mind, OnePlus is giving up on all StyleSwap covers.
If you have a One and really, really want to swap out the back cover, the company will be selling off its small stock of bamboo covers that did pass inspection. There are no details on when that will happen, though. As a post-script, the forum post notes that OnePlus' experience with this defect will make sure we won't experience a similar disappointment when the "OnePlus 2" comes out.