It made no sense in the first place
The Android OS itself has provided an endless stream of exploitable bugs, and it's not like Silent Circle was going to audit and harden that code base to the point where the phone itself was uncrackable - not to mention the massive resources required to stay on top of updates. As bad as Google and even its large OEMs have been, it's hard to say how Silent Circle could be anything other than worse without an enormous user base (at least Samsung Galaxy size).
A phone that's more secure than mainstream IOS / Android is probably impractical at this point, because the device itself is now just the center of an ecosystem of apps. The only company with a prayer of getting any traction there is Microsoft and they seem determined to commit suicide instead. For anyone smaller, the window is pretty much closed unless they can pull off a fully sandboxed emulation layer (like Android as a hypervisor guest, which would be awesome).