First, thank you for all of the feedback - your thoughts are appreciated and have significantly impacted the decisions that we’ve made about how we move forward.
TL;DR - We will be retiring the beta site shortly and will be removing the button to get to it and ceasing support for it.
We will not be migrating the unified posting experience to the main site. Not migrating the unified experience to the main site will obviate the need to solve the issue around the conversion of comments and answers to “replies”, because that was tied to this unified post experience.
Source [web-archive] ✨
Preview of the button "Beta"
One month ago, I posted a comment with screenshots and my opinion. It also links ot the official Stack Overflow resources regarding it.