I may not like the Chrome monoculture happening at the moment but that doesn't mean Chrome is the same dumpster fire that was IE. And Google are hardly going to let Chrome stagnate when Chrome is the perfect vehicle to local users into Google's non-free ecosystem (I say "non-free" because you pay with your privacy)

But if we want people to stop being locked into Chrome, the best way is to cease to support it. If stuff works in Chrome, that'll be because Chrome supports web standards properly, and not because there's some proprietary random Google standard-they-just-came-up-with that it relies on. (I'm looking at you, <portal>.)

Don't contribute code to Chromium; instead, contribute it to a popular fork (like ungoogled-chromium), or a different browser altogether. Until Chromium is a less-centralised project, you're pretty much just giving a competitive edge to Chrome, and hence Google's near-monopoly on the web, without Google having to put in the resources to do it themselves. You're working for Google for nothing.