It could help, depending on one's goals - one of the most notorious issues (or features, depending on who you ask) with the Linux development process is ruthless interface refactoring which requires device drivers and board support packages to be in mainline or to become stale almost instantly.
A smaller surface area with a stable HAL would separate the proprietary / often bad board support code from the kernel itself and allow core changes to progress without requiring software-adverse hardware manufacturers to keep up.
Whether or not this is a good thing is certainly debatable, but I'm not convinced the Linux "get to mainline or get wrecked" approach has stood the test of time well.
A smaller surface area with a stable HAL would separate the proprietary / often bad board support code from the kernel itself and allow core changes to progress without requiring software-adverse hardware manufacturers to keep up.
Whether or not this is a good thing is certainly debatable, but I'm not convinced the Linux "get to mainline or get wrecked" approach has stood the test of time well.