The next preview release of the SmartSDR and 6x00 firmware was due out about now, but apparently this will be a little delayed now due to some quality issues detected in this cycle.
Flex operates several phases of development and testing. Each cycle will produce builds that are sent to 'alpha' testers, then to a wider set of 'beta' testers if a build looks solid. Finally, if the beta testers are happy then a good build will be released as the next preview release. Thus, preview releases are supposed to be somewhat stable and usable (modulo a set of supported features).
While I'm chomping at the bit to test the next version, especially if it has the signal path optimisations we've been promised since our initial testing, I'm glad they're making sure we are moving forward with solid releases and not just letting releases 'escape' that have significant issues.
Flex are currently saying that they're on track for an end-of-September release of the V1 software. That's good news, but as far as I'm concerned I'd rather they continue the prerelease incremental developments until V1 is completely ready. By that I mean fully delivering on the expected level of receiver quality for SSB, CW and AM and generally solid in terms of the client UX. Anyway, we'll see what happens soon enough I suppose.