The issues (spontaneous reboots, etc.) identified in the Spectre mitigation modifications made to the processor microcode have caused Intel to pull back the already-released microcode and to reset their delivery schedule. The schedule for the delivery of updated BIOS releases for the NUC products will be announced once validation of the new modifications to the microcode is complete. The schedule, once established, will be published on this page: Intel-SA-00088 for Intel® NUC, Intel® Compute Stick, and Intel®.... Watch it for updates...
Here is the latest announcement from Intel Corporate: Root Cause of Reboot Issue Identified; Updated Guidance for Customers and Partners
For completeness, here is the larger set of schedule pages related to INTEL-SA-00088 and Intel board and system products:
Unfortunately, as of today, they really don't tell you much...