As for the sempai-kohai issue over time in Aikido, I guess it doesn't matter to me, not sure how it would be an issue. I've been in so many dojos, and been up and down the rank scale so many times, but it has never been an issue to me. I don't like 'mat instructors', if that is the problem you have with a 'junior' sempai...I just ignore 'mat instructors' no matter what the rank (usually it is pretty low, funny how that is
) Personally, I prefer to learn by watching/feeling/doing, and dislike a lot of spoken instruction.
But if it's just a matter of who goes first, who cares...I'm currently at a dojo with a philosophy that disturbs me enough, that I don't test for rank here. I've seen quite a few pass me in rank the past year, and it's fine with me (although I do envy the chance to test...sigh). I happily let them go first, and they know that if they didn't get it I will show them once and then let them take their four turns...but maybe rank means something different in your dojo, or to you.