So, from what I have read, nobody actually knows that OEMs would use this to lock out alternate operating systems, but rather they are afraid they will.

If they do, that is fucking insane. There seems to be no end to the locking in of revenue streams. Big Media has steadily dismantling the concept of ownership, where the movies, books, and music we listen to is just rented, and we never actually own it. They are increasingly attempting to get rid of the concept of even owning an original copy, -a dream finally able to be realized in the digital age.

And you see the trend even with manufacturing, where OEMs lock your gear down, and lobby to make it illegal to alter your own gear or "jailbreak" it. Before long I expect to see more instances where people are "sold" physical items (like a computer itself) along with fine print stating that they don't actually own it, but are rather leasing it indefinitely, or something along those lines.

So you'd think I would be rabidly in favor of open architectures and open source. I am to a point, but only to a point. I actually think that it is plausible and useful that systems like the one described in OP's article are beneficial for the end user. Apple basically is moving to the model on OSX with sandboxing, which software designers have to respect if they want the privilege of selling to me via Apple's Mac App store. I like this as a consumer. I like that programs have some minimum vetting from a security perspective. I like it on iOS, the fact that apps must be reviewed and that the instances of malware on my phone, which contains far more sensitive info than my desktop ever would, are going to be lower than on say, Android. Right now OSX's sandboxing is optional and applies only to the Mac App Store, but the same worries are being voiced by technologists. As long as users can still grab from devs outside of the app store chain of distribution (go direct), I see it as the best of both worlds. iOS is even more locked down, but that is one of the best features of iOS from my viewpoint as a consumer (many rabidly disagree).

At any rate, there are great arguments for UEFI SecureBoot, as well as great cause for concern. It isn't black and white in my view, and unfortunately, mitigating the concern involves trusting large corporations to do the right thing. When user rights but up against corps chasing revenue, bad things happen.