For those interested, Jono wrote a piece:
The post itself includes a highlighted screenshot of the installer screen in question:
The most intriguing suggestion mentioned on that blog is a (very beautiful) mockup, showing a slider from "free" to "non-free":
All free software → proprietary drivers ↔ MP3 ↔ DVD ↔ Flash ← All non-free software
This would make the choice less binary; and allow the installer to call-out at edge level what the impact on the user-experience would be.