Ever since Jonathan Eastabrooks introduced this goal of a buoyant voice (we had some discussions before that I can't find right now), I first came up with Luther Vandross for the male voice. I am now just in awe of Azealia Banks... https://www.youtube.com/watch?v=au8QGTiPhEw  How can we ever reach just a little bit of such perfection?

Great examples! When I think of bouyancy, I think agility, flexibility, and enough lightness to move quickly. And all that (for me) means (1) vocal exercises that move quickly and cover a wide range, so your voice also has to move quickly + accurately and (2) training head voice for lightness and flexibility throughout your range. 

Yes, that makes sense, thank you. And it's mainly this lightness in the listeners' ears what is so impressive. How to train this lightness, specifically?

Training on a quiet OO or EE vowel throughout your range will help you achieve that lightness. If that still feels too heavy, I also like singing on an NG or NN (which ensures you have some head/nasal resonance). All of these configurations make it easier to sing "lightly"!

Thank you Camille for that helpful additional tip.

My pleasure, Steffen!