I'd expect the opposite. It's likely not worth funding someone to reimplement a whole browser engine instead of reusing an existing one. It would take a lot of time and money to build and maintain and you don't gain too much by having your own entirely custom engine.
There's a difference between forking a full browser (this is quite easy initially, but down the road your fork may end up being difficult to maintain) and building a new browser on top of the rendering engine (Blink here, could be Gecko or Webkit). In the latter case, the initial investment is higher, so getting to a daily driver product requires more effort. However long term that can be beneficial because you don't conflict that much with upstream changes.
Writing a new rendering engine and browser on top is totally different effort as you may guess.