Very true points, as all creatively working people, designers and front end developers do look around for inspiration and ideas to copy. That is obviously a reason for a very unified look across many websites.

What I wanted to share is a thought I had when you said that one day there might be other shaped than rectangles on the software side of things. There are: Your circle goes here. You can use SVG to draw any given 2D shape you can imagine and even fill those shapes with text. So there already is the technology and embedded SVG is actually accessible by software and therefore potentially accessible by screen readers, search engines etc. Its just a question of front end developers and designers picking up the SVG-Element's abilities to get started on a web that no longer has rectangles backing it.