Because in this case it is open? I'm not for having a single implementation but I wouldn't complain if every single browser used the same engine. It still won't

Because in this case it is open? I'm not for having a single implementation but I wouldn't complain if every single browser used the same engine. It still won't be ideal but this by default removes any incompatibilities (assuming the same branch of code is used--a potential problem that will crop up).