From their beginning, the first (and one of the biggest) complaints about the OnePlus One was how difficult it was to get one. OnePlus' quirky invite system has been very unpopular. Luckily, they are wise enough to recognize this and have been working on a new pre-order system that they expect to implement in October.
Here's a quote from OnePlus during a Reddit AMA,
We are working on a pre-orders system, we were initially aiming for September but it’s been slightly delayed, hopefully we’ll be ready to launch it in October. ~ OnePlus
It's good to see the company is still evolving. Perhaps they will be able to work through all of the issues which have plagued them up until now.
As a sidenote, in regards to the different back covers originally planned for the device, and particularly the Bamboo cover, OnePlus has run into another problem. Here's a quote regarding that issue,
The Bamboo StyleSwap Cover has been delayed following the discovery of a “minor flaw” in the cover. A launch date has not yet been rescheduled for the Bamboo cover and there is not any news on the other handset covers yet either. ~ AndroidAuthority