@codinghorror I apologize for replying again, but I did some digging through the Discourse code on GitHub and some debugging, which led me to a simpler suggestion that I hope will be less contentious.
My investigation on GitHub and debugging in the Chrome console was around trying to figure out if there was anything I could build myself to achieve the functionality I wanted. The short answer seemed to be no, but this investigation did lead me to an attribute used for the reply-to-tab widget called replyDirectlyAbove. The attribute seems to be exactly what I care about, but right now this isn’t exposed anywhere that can be interacted with publicly.
Basically, my new proposal is to add a class on that widget when attrs.replyDirectlyAbove is true. For example:
<a class="reply-to-tab reply-to-post-directly-above">
...
</a>
With that addition, individual Discourse installs could choose to introduce custom CSS to display that differently from the regular reply-to-tab, but there would be no need to change anything by default across all installs.