Very interesting if true.
It's not a big cut, but there have been smaller which have warranted full name changes. The 290/390 are actually very slightly closer in shader count to the 290X/390X than the GTX 1060 3GB is to the GTX 1060 6GB.
Heck, the 980 Ti is even closer to the Titan X than this (and even closer than 290->290X). It has half the memory like the 1060 3GB... is actually closer to the full chip than the 1060 3GB... but received a different product name. When you look at it in that light, a bit odd to be sure!
Historically this is not unprecedented though. The 460 launched with two different versions, but they at least had the same shader count (cut ROPs and buswidth). The reduced shader 460 SE was released months later and, of course, had SE tacked on the name.
Some other cards with the same name and different configurations, including shaders, are the 9600GSO (5 months apart) and the 8800GTS (13 months apart). But the different versions of these were actually completely different chips, and released much later.
Personally I don't like it since it can create confusion. I thought the GTX 260 Core 216 should have been named the GTX 265 or 270, although at least that was a replacement and not a simultaneous launch.
