Like I said, I can very much see from my experience that a good quality square taper like a un55 in a good frame, properly installed, will most likely be forgotten for a long time, and that's great.
That said, I like the idea of learning more about external bb's, as they certainly are on lots of bikes, and I don't want to unaware of different external bb's if they indeed can have good longevity.
I really enjoy working on bikes too, so also want to learn more about what I don't know.