Just hang in there - there's lots of happening with extension community. To begin with: Firefox and Edge are jumping on webextensions right as we speak. Chrome extension site and Firefox extension site will defo be the places to get extensions in the future. If one doesn't find from Opera Addon - then go to Chrome Web Store. There's also React and Redux which are new extension/app platforms to run in the browser. Just stay tuned.
And you know - not that long ago Chromium, then Chrome, enabled settings_override API. It's poisoned to come to Opera as well.
Interesting times ahead for a web browser!