I just finished building a couple of prototype speaker stands back in the middle of June, where the speakers sit on the top shelf and the amplifier on a lower shelf. The amps are not hidden (not a requirement for me) nor is the angle of the speaker shelf adjustable, but it wouldn’t be too difficult to incorporate either option into a stand.
A speaker stand with room for an amp?
I have rather large 2-way stand/bookshelf speakers and I'm thinking of going 100% active with them. They have an external passive crossover already, so there's nothing to rewire internally. What would be nice is if there were room for a small Class D stereo amplifier to be hidden in the stand. Even better if it was adjustable for angle.