If you wanted to give OxygenOS a try on your OnePlus One prior to doing the full update, you can now give it a test run on MultiRom. The new OnePlus rom has been ported over by developer "KINGbabasula". This build is apparently still pretty buggy, so this won't necessarily be a daily driver experience, but at least this will give you the chance to try this new rom out. This build is apparently meant to be ran as a second system only. It also looks like the developer had to implement all kinds of hacks and fixes just to get this to boot. It may be better to just wait for a full port as I'm sure that will be just around the corner for many phones. If you just have to give this a try now this will be the way you can do that!
Via XDA