Basically, I see it this way:
- You can be MitMed broadly, like the Xfinity case, but the company in question can't really do anything crazy like inject viruses or do something that would cause the user to actually notice because then their ass is going to be on the line when it's exposed that Comcast installed viruses on millions of computers or stole everyone's data.
- Or you can be MitMed specifically, which will cause professional detriment, but would require someone to specifically target you and your users. And I don't see this as that likely for the average Joe.
Really, what I would like to know is: How realistic is it that I, as a site owner, will be adversely affected by the MitM that could theoretically happen to my users on HTTP?