First news broke at the Develop Conference in Brighton, as Martin Fuller from the Xbox Advanced Technology Group, said of the concept of being able to turn retail units into devkits (and vice versa):
"As far as I'm aware there are no plans. I'm not aware of the reason why we didn't manage to do that."
"We were in the early stages of Xbox One looking at the idea of a retail kit that could be turned into a development kit, and vice versa. In the end, although that was a very admirable goal, it hasn't happened unfortunately. Can't tell you the specifics of exactly why not."
Apparently "as far as I'm aware" was an important caveat as Microsoft later issued a statement to Polygon:
"The comments today were inaccurate. We remain committed to ensuring the best possible solutions for developers and hobbyists to create games for Xbox One. We will share more details at a later date."
The ability to turn a retail unit into a fully fledged devkit would naturally open up Xbox One development to even more indie developers, so let's hope Microsoft can sort it out.