Both Williamson and Otala advocated this approach, but they did it for different reasons. Williamson for stability reasons (circa 1947) and Otala for TIM reasons (circa 1970). I think once you get the TIM thing nailed, it's all-or-nothing. This is what Baxandall demonstrated circa 1978. Both stability and TIM will militate against this approach, but the design challenge is facinating.
"But I've always wondered what those amps would sound like if they didn't use feedback (you'd probably have to do an extensive re-design of course). I don't think I've ever heard a well executed tube amp without feedback. Have you? Could be interesting..."
I can't think of a single famous-name golden-era amp that was designed without loop feedback. Even the Brook 300B amp used it, although its designers were suspicious of it (AE, June 1947). Somebody correct me if I'm wrong.
With modern amps it's a different story. If you've ever heard an Atmasphere you've heard one. The latest contender is the Antique Sound Labs' Hurricane, as reviewed by HP. The Hurricane is a classic Williamson circuit (with octal tubes no less, just like the original) minus the loop feedback. There is no allowance made for excess gain so the sensitivity goes to the moon (in the British style).
Virtually all of the SET amps that have appeared in modern times are feedbackless designs. Most of these trace their lineage to the Western Electric 91A theater amp:
http://www.aloha-audio.com/library/schematics/we91a.jpg
Sometimes you will see feedback controls in these modern-day SET amps that allow up to 10dB to be applied. Unfortunately this violates the multiplication hump rule, but how many of these designers understand what that means? They hear a degradation and then exclaim: "Feedback is terrible!" A little knowledge can be dangerous.