As impressive as chakra is, V8 is the same in contrast to edgehtml to blink, they don't see the value of fragmenting support, and V8 really is getting very powerful, a blink+chakra browser would likely be more of a nightmare to developers
They already had chakra working with nodejs.
Rendering engines are mammoth projects. I’ve contributed to Chakra, v8 and nodejs. They are somewhat manageable codebase. Blink codebase is insane.