Wait, I think you might be on to something. I am going to assume that the "upper classes" were comprable to nobility. They were the wealthy patrons, land owners, etc.
Although we even more wealthy individuals now, they can't be compared in the same way to those of old. But, there are entities that might be similar. They are called corporations.
An economic crisis would not be a point in time to start asking for more money from corporates, but other crises might best be handled in that way. Practical? I don't know, but maybe worth exploring.
I have to make one correction to my agreement with the government using only 6% of GDP. I think it might good to have a slightly higher percentage that would allow the government to run a surplus (maybe accounting for 8-10%). This way if the Fed can no longer cut interest rates to provide fiscal stimulus, a tax cut remains an option.