Yeah, Electron and Chromium fill a close enough niche that I don't think the market is really demanding what I envision.
Try giving foobar2000 a spin or checking out some screenshots to get an idea for what I mean. Unlike Chromium, the browser should be extendable, at runtime, via a component system and editable layout tree. Runtimes, backends, common libs, fonts etc should be managed using a repository system.
Chromium requires recompilation (and know-how) in order to make any big change. Comparatively, a user should be able to completely reskin their browser, switch JavaScript engines, etc. on a per-domain, per-group or per-tab basis in seconds without restarting the browser.