Essentially, he asserts that computing (or computer science even) isn't a real field (like biology or physics). Most people can't name the early computing pioneers whose work they build on (not true in Physics or Biology, we celebrate the pioneers) nor are they familiar with the work that was done in the Xerox PARC days.

It's gotten so bad that a lot of computer science research just assumes that what we have now is what's going to remain forever. In the 70's, all kinds of interesting ideas and experiments were tried.

Hardware implemented VM's, direct manipulation programming, OS-free computing environments, highly re-configurable computing a la FPGA's, and hundreds more.

Nowadays, we think that creating custom ASIC to run machine learning algorithms quicker is innovative and novel.

All this to say that many of the ideas in Dynamicland aren't new. They're rooted in ideas that are decades old. If you look at Bret's papers he uses as references frequently, you'll notice how many of them are over 10 years old - http://worrydream.com/refs/