"Quantum computing has long seemed like one of those technologies that are 20 years away, and always will be."

I've just completed a PhD in this area, and I've never heard this sentiment before. It seems quite unlike fusion research, which is famously always 50 years (?) away. Quantum computing research is proceeding at a rapid pace, and actually it is perhaps only 20 years old in total. Although Feynman considered something akin to a quantum computer in the 80's, it really wasn't until the 90's that quantum error correction became a thing. So it really is a very young field of research. The "old-timers", they are all about 40 years old now, unlike other areas of physics where the oldies really are very old!