It'll be OS 11. Why? Thus, meaning that Apple will most likely omit 10.10, as it ends in a zero, and because Apple has already released a 10.1 (remember 10.10 would be "10.1" according to Apple's naming convention) the next logical step is to move onto OS 11. I think that Mavericks was supposed to be OS 11, but because iOS 7 needed more attention, they decided to delay the redesign, but kept with the name change. Don't tell me about how the logs say Apple is testing 10.10. Apple can easily fake version numbers to hide version they're actually testing. After all, Apple wouldn't want traffic tracking software to reveal OS 11 before it's reveal.