Well, that is a loaded question. To best answer I would say you have to divide it up into commerical amps and DIY amps. Unless you get into real high voltages high power amps basically require feedback because of the need to use pentodes. Doing feedback right isn't so easy and the average DIY type lacks the experience and equipment to do a top notch job. I doubt you or I would ever dream up the citation schematic now would we? So for DIY stuff I might set a limit at around 30 watts and ideally more like 10 so we don't have to leave class A operation.Now when you get into the commercial area all bets are off. Have you ever looked at the Wolcott white papers? Interesting reading. I always wanted to hear one of the electronluv amps too.
But yes, the citation is a special amp the likes of which I doubt will ever be reproduced again.
Russ