I received a beta invite for Classic, and had also been an alpha and beta tester for the original game 15 years ago. That isn't unique; plenty of people in Northshire Valley had had the same experience, suggesting to me that active players who were Day 1 WoW gamers or had participated in the original tests might have gotten priority invitations to this one.
The primary goal of Conflict and Strife is to provide an interesting choice in PvP by allowing access to an extra PvP Talent. It’s not necessarily going to be a strong option for PvE. The acquisition of this Essence is via PvP, and is totally optional for PvE-focused players. While there may be interesting PvE uses for some of the choices, it is not expected to be a strong competitor on usual PvE criteria (like total throughput) on every spec.