Update: Microsoft responded to our request, ensuring that Windows 10 testers personal data is safe, though neglected to confirm whether or not this "feature" would be present in the final release of the OS.
"As always, we remain committed to helping protect our customers' personal information and ensuring safeguards are in place for the collection and storing of that data. As we get closer to a final product, we will continue to share information through our terms of service and privacy statement about how customer data is collected and used, as well as what choices and controls are available."
Next up, in regards to keylogging, the policy specifically states that "If you open a file, we may collect information about the file, the application used to open the file, and how long it takes any use [of] it for purposes such as improving performance, or [if you] enter text, we may collect typed characters, we may collect typed characters and use them for purposes such as improving autocomplete and spell check features."
Lastly, if that's not enough, Microsoft is also able to "use information we learn about your interests to help make the ads we show you more relevant, and we use your voice data to improve speech recognition."
We've reached out to Microsoft to ask them what safeguards are in place for user's personal data, and whether or not this data collection technique will be used in the retail version of Windows 10.
Users signing up to the a test version must be aware that Microsoft is going to collect a lot of data on them, but I doubt they would have thought the company would go far enough to install a flipping keylogger on their machines.