As long as Chromium is open source, either filter lists will be supported in the new add blocker or someone is going to fork Chromium to keep list-based adblock support.
Is Chromium actually used by many people? I was under the impression that people mostly use Chrome because of Google's advertising & bundling. [1] supports my theory with desktop Chrome amounting to ~25% usage and Chromium amounting to ~0.03% usage.
Some people use it. I think it's especially common on Ubuntu since they have it in their "Software center", whereas if you want to get Chrome proper you have to go to their website and get the .deb.
However, as you say, it's a very small % of people. I think most people don't even know Chromium exists, let alone what the differences are between it and Chrome. That might change though if Google starts abusing their position and doesn't get this ad blocker right.
I've been around long enough to know that no browser dominates forever, especially if companies start taking their users for granted. It happened to Netscape, IE, and Firefox. It could happen to Chrome too. If they screw this up I'm going to a Chromium fork + uBlock Origin. :)
I use Chromium on macOS for development and occasional browsing. Chrome Dev Tools is really in a league of their own. But my primary browser is Safari, because it performs much better during regular usage on my 2012 retina macBook Pro which only has a paltry 8GB RAM.
On my mobile android device I use Firefox, since it allows you to install extensions. Running uBlock Origin makes mobile web a vastly superior experience. I also use Firefox on Ubuntu and Windows, since it has the least invasive defaults and it lets you easily sync content across devices.
I think browsers are actually in a great state. People have lots of incredibly high quality options to chose from! Although I'll admit I'm a bit worried that there appears to be a bit of a Chrome monoculture growing.
