Maybe removal of binary interfaces should be is for a major release? Name the next kernel 3.0 where this, and maybe other obsolete interfaces, are removed! New functionality is added continuously, and there will probably never be a "major" step in that sense. But cleaning out of obsolete stuff could make sense to distinguish like this?
Or at least a 2.7 series, which drops compatibility with 2.6. That would be another way to give back some meaning to the first two numbers in the kernel version number.