The actual Uno (i.e. AVR-GCC) toolchain I wouldn't expect to change a lot. But they do have a habit of releasing a crapton of boards on different uC archs. And

The actual Uno (i.e. AVR-GCC) toolchain I wouldn't expect to change a lot. But they do have a habit of releasing a crapton of boards on different uC archs. And the libraries are written mostly by 3rd parties.