At this time, the closest thing to a source is "Some Czech guy did a traffic analysis of data<link to an unrelated disclose.tv page> produced by Windows 10, and released his findings the other day."
This is just appalling journalism if nothing else, and hurts both sides of the case.
EDIT: I retract some parts of that. The link to the source (in Czech) is tucked away discreetly at the bottom of the page: http://aeronet.cz/news/analyza-windows-10-ve-svem-principu-j...
It was discussed in the top comment and the replies to it: https://news.ycombinator.com/item?id=10053420
At least they plainly state at the beginning of the article: "Note: Some readers have commented that the original source for the article is of questionably validity. If anyone can confirm or refute the original author's finding with actual data, please let me know in the comments, and I'll update this post accordingly."
It would be good to see something confirming any of this. Even if all of this article's claims are false, it would be good to see a deep dive into exactly what is actually being sent and when.
There's already lots of commentary there on the results.