>it appears that most of the barriers to a cryptographically-relevant quantum computer are engineering challenges rather than underlying physics
I've heard this 15 years ago when I started university. People claimed all the basics were done, that we "only" needed to scale. That we would see practical quantum computers in 5-10 years. Today I still see the same estimates. Maybe 5 years by extreme optimists, 10-20 years by more reserved people. It's the same story as nuclear fusion. But who's prepping for unlimited energy today? Even though it would make sense to build future industrial environments around that if they want to be competitive.
I've heard this 15 years ago when I started university. People claimed all the basics were done, that we "only" needed to scale. That we would see practical quantum computers in 5-10 years. Today I still see the same estimates. Maybe 5 years by extreme optimists, 10-20 years by more reserved people. It's the same story as nuclear fusion. But who's prepping for unlimited energy today? Even though it would make sense to build future industrial environments around that if they want to be competitive.