Also not every generation transition is as clear-cut as the 4th to 5th gen transition (what with all the stealth characteristic geometry requirements). The transition from 5th to 6th will be much more murky akin to 2nd-3rd gen transition probably if the 6th gen doesn't come to be defined by variable cycle engines. Even then it will not be as incisive, since you will be theoretically able to replace the engines of your 5th gen fighters with minimal design restructuring. What could potentially make it more of a sharp difference between 5th and 6th gen is a possible transition to a more flying-wing configuration as manifested in several conceptual arts. Because then you can't make your 5th gen fighter into 6th gen, just by replacing components.