We just reported of a new Windows Phone version 8.15.12492.0 that appeared on WP Bench and which was starkly different from the current Windows Phone 8.1 versions.
And news are now coming in that a build closely resembling to it, 8.15.12492.41 is rolling out internally at Microsoft for final testing. This build is being referred to as Windows 10 Technical Preview for Phones, the one that you have been waiting so desperately for and is being tested by some 1000 testers internally at Microsoft.
Whether Microsoft will release Windows 10 Technical Preview for Phones under the same version is not known but looks less less likely.
It is also being reported that once after the successful installation of above update, the splash screen that says Update Successful has a quote which reads
Every setback has a major comeback.