Pluton is not (currently) a threat to software freedom
At CES this week, Lenovo announced that their new Z-series laptops would ship with AMD processors that incorporate Microsoft's Pluton security chip. There's a fair degree of cynicism around whether Microsoft have the interests of the industry as a whole at heart or not, so unsurprisingly people have voiced concerns about Pluton allowing for platform lock-in and future devices no longer booting non-Windows operating systems. Based on what we currently know, I think those concerns are understandable but misplaced.
As usual, Matthew Garrett does an excellent job explaining complex topics like this.