It's easy to get daunted at least. A realistic scenario could be something along the lines of: get content onboard by securing some buy-in from some heavyweigh

It's easy to get daunted at least. A realistic scenario could be something along the lines of: get content onboard by securing some buy-in from some heavyweights, for a reduced feature set. Maybe convince a incumbent browser vendor or two to also provide a safer kernel for that content profile. Then targeting that feature set with the new implementation, and supporting a compatibility mode fallback to a legacy rendering engine for other web content. (VM-based or remote cloud based sandboxed rendering for the fallback?) But the above would of course have a much better chance of taking off if there was a promising start of an implementation first, so it's not necessarily a reason to wait for the big boys before working on it. (I wonder if Servo could be a starting point?)