Agreed and well stated. However, since, the concept of "familiarity" will continue to change, how will modern UI designers understand what their end-users know,

Agreed and well stated. However, since, the concept of "familiarity" will continue to change, how will modern UI designers understand what their end-users know, relative to what they should know? In order for the design to evolve, people must often be led. I whole-heatedly agree with you that simplicity is a relative term, but truly finding the nexus of your users' understanding vs. what they need to know is difficult.