No, I actually wasn't aware of that feature, till you pointed out. Not a very intuitive place to hide that option though.
After playing around with it for a bit, on the surface it seems to satisfy most of what I posted in the suggestion, but after some experimentation, it seems pretty glitchy, and somewhat cumbersome.
The always on top option is there, however it seems to stop functioning after I move the window. It gets rid of the speech engine settings, which is good, but it also ditches the toolbar (which I would most likely keep on).
You can't use the window to edit the contents. I know it's because you can proofread contents from other applications as well, and the proofreader has no way to interact with the other app to change the contents. So in this sense, this is probably the best that can be expected from the proofreader when reading contents from other applications.
But if we're using the function to proofread textaloud contents, it adds a lot of unnecessary keystrokes. Instead of my ideal scenario, where I see a mistake 2 lines below, I move my mouse over there, correct the mistake on the fly without having to stop the reading... I would have to select text, start the proofreader, and when I see the mistake, exit out of the window (which puts the focus on the voice selection dropdown menu for some reason, so the instinct to mouse wheel down will change the voice), find where the mistake was, correct it (make sure to clear selection beforehand, as not to overwrite the selected portion), reselect the rest of the text and resume proofreading.
With the normal window, I pause reading via hotkey, correct mistake, and resume reading. No searching for where the mistake was in a possibly large selected text, no fiddling with constantly reslecting the text, and less of chance I'll end up overwriting text by accident. Compared to this, the speech engine settings taking up half of the resized window, and using a 3rd party "always on top" app seems like a minor inconvenience.