> Do you think what's seriously lacking is, for some expert to sit down with H&P and gem5, implement a ton of modern features, analyze them, and write a big textbook about it along the lines of 'Practical Computer Architecture'?

That would certainly help. Another good step in the right direction would simply be taking a processor with a good mix of modern features and giving a guided tour. Everything is done by something, so show all of those somethings and how they're put together, and how they all fit together into a complete design.