Skyrim was released on November 11, 2011. Creation Kit was released on February 7, 2012, although originally planned for January 2012.
Fallout 4 will be released on November 10, 2015. GECK will be released on February 6, 2016?
Doesn't matter to me. We'll be modding Fallout 4 long before the new GECK comes out.
I uploaded mod #1859 to the Skyrim Nexus on November 27, 2011—just 16 days after Skyrim was released—and then #2311 on December 1 and #3313 on December 11. From those numbers, you can see how quickly we started growing the Skyrim Nexus. Two weeks after Skyrim was released, and months before there was a Creation Kit, there were nearly 2,000 mods. Fallout 4 will crush the Nexus, so hopefully, Bethesda.net can alleviate some of that burden.
In the meantime, I'd still like to get an early peek at scripting for Fallout 4.