The "moment of truth" will probably start to appear in 2020 as manifest V3 goes "live" in Chrome generic distribution. Then we'll start to see whether/if the ripples spread into non-Chrome chromium (and thereafter potentially impact other chromium-based browsers).
Per https://www.bleepingcomputer.com/news/software/google-begins-testing-extension-manifest-v3-in-chrome-canary/ , 1 November 2019: "While they are now in preview, Google expects the manifest v3 to go live in 2020 with the v2 end of life to be determined in the future."