There's really nothing to stop another ARM licensee making more powerful ARM processors, there's no special Apple pixie dust, it's just a matter of investment. The other licensees just got lazy and psychologically trapped by their price models into thinking in terms of deterministic, incremental annual performance and feature improvements. They 'knew' nobody else would break that cycle because the margins weren't big enough to support the investment needed to jump so far ahead. If the margins and volume in fast efficient ARM laptops are there, then there's nothing stopping them from happening.