After the current version 9.3 FreeNAS 10 will follow. With the upcoming version, there will also be some innovations that further improve the free NAS operating system.
FreeNAS 10, which passed the second milestone release (M2) on July 06, 2015, will not simply be an evolution of the previous FreeNAS 9.x but have a completely new architecture and structure. The known features like the OpenZFS file system, the possibility to extend the functionality with Plugins to improve.
Major innovations will affect the user interface, which will be according to the FreeNAS developers will be more of a web app than a UI in version 10. The changes to the architecture should also make it easier for FreeNAS developers to continue developing the system, so new releases will be easier.
There should be a total of five Milestone releases, currently, as mentioned, the 2nd appeared. So it is still some time until the final release - there will probably be no new FreeNAS version before 2016. The first "public" demo for interested users (who have a test system, because with live data you should definitely keep your hands off these early FreeNAS versions).
FreeNAS 10 will of course have similar system requirements as its predecessors: a HP Proliant Microserver N54L or the current issue in the form of a Microserver Gen8 will also work fine for FreeNAS 10.