Unless you have the resources of FAANG, forking Blink is a pipedream. Brave doesn't have the resources, and Microsoft already gave up that dream. Web Browsers are insanely complex and fast moving; and maintaining a "living" fork of Blink is difficult as upstream doesn't make it particularly easy to downstream changes after you've made any sort of modifications.
Which ironically, if say a major platform that everyone had to support slowed down their pace of development to be more conservative so you couldn't jump on features released two weeks ago that would be better for the browser landscape as a whole.