Two popovers on this blog are *REALLY* f-ing annoying to say the least. When looking at more than once a day, extra so.
If I want to share, I'll copy the address bar, or find a way. If I want to subscribe, I'd probably figure that out too. You're reaching a technical audience and these types of engagement patterns are a distraction to say the least.
I would suggest a fixed box in the lower right with a the standard share glyph/icon and a subscribe with an email glyph/icon. When clicking one of those, then have the popover dialog come up. NOTE: make room for it when scrolling to the bottom so it doesn't interfere with your footer.
row-reverse isn't the same as right alignment, it reverses the direction. justify-content on your #3 would be how you would align right.
Other than that, decent writeup.