I must comment (with some delay) that the cookie dialog blocker was an awesome idea, if there's a chance you expand it to block "download our app" banners that some websites insist on spamming (Reddit is a prime example) it'd make Opera more attractive. It's an old problem we mobile web browsers have to live with: https://thenextweb.com/shareables/2013/05/12/this-tumblr-says-what-everyone-is-thinking-i-dont-want-to-download-your-app/
I also want to note that I used to be a fan of Opera's tab switcher but it has been worsened on each iteration (it used to display more tabs on-screen now it's 3 AFAIK). Nowadays it feels slow to use (the screen transitions between the open page and the switcher, plus the vertical swiping and one more tap to access the tab I want) and the thumbnails remain blank until you first switch to the tabs (open in the background) making the useless.
Practically I'm not a Opera mobile user anymore because the Yandex browser for Android just feels faster to use, yeah I know, it's a list of tabs but it's a matter of simplicity over form that makes operating the browser faster (just get out of the way and let me use the websites haha), and it also has some good actions to manage tabs in addition to Close all, like Close all tabs above / Close all tabs except the current.
The whole UI on the bottom including the address bar is another factor that makes me stick with Yandex, and when I start to use the page the UI compacts and gets out of the way and feels like it's not there anymore but it's still easily accessible with a tap or swipe, it's just magic... But I still kinda like Opera and your ideas, I'll be watching your next steps.