With XFO, doing something like adding 'reddit.com/' before the domain to see if it's been submitted becomes much more computationally intensive on reddit's side if they can't just put it in a frame. This is where I run into issues mostly, with tools such as that. That said, there are other things it could do (take me to a submit page or a discussion page instead of framing the page). And frames suck anyway, so there is that.
I can see the usefulness in CSP, I just feel like it's a band-aid on larger problems.
I am rather curious where did you get this claim? Any stories I should check?
And also what's the larger problem? Again, I'd really love to hear you elaborate on your thoughts.. thanks.
Also, it's my user-agent, it's suppose to do what _I_ want it to do, not what the content author wants it to do, and I can't find a way to disable honoring XFO.
For CSP, one example of a larger problem would be excepting and storing unsanitized input. If it's going out to the user as (otherwise executable) javascript, are there other places that you're placing unescaped user-submitted data that could be an issue (a sql statement perhaps or the API to a site who trusted you to sanitize things (although they shouldn't)?).
* XFO, it you're doing API first there really is very little reason to frame a page. Maybe Twitter style widget support? But in that case you can have a separate URL for that.
* XCTO, yes, welcome to the 'organic' web :p
* HSTS, the first connect is difficult, maybe one day via DNSSec? But I must confess to know very little about DNSSec.