The old "Velocity Diet" from t-nation was all shakes and like 1 whole food meal per week and then it turned into 1 whole food meal per day.
I believe Skip Hill did an experiment with willing participants where he had them get all of their protein from shakes, but adjusted carb sources and included fiber from veggies. All participants did very well from what I recall. I had a friend do the experiment and it was the best he has ever looked and honestly, since then his physique has gone to shit LOL
I do feel a mix in amino acid profiles is beneficial and as long as you are using the right supplements to ensure the micronutrients are covered and you get enough fiber and overall macros, then I don't see an issue. If doing this, I would suggest using various types of proteins, e.g whey isolate, micellar casein, milk protein isolate, beef protein isolate, egg protein... and even some plant based proteins like rice or pea protein to get a variety of amino profiles as one would when eating meals of chicken fish, beef.. etc..
I agree that having a mix of different protein powders would work best. I like that idea.
I never heard of the velocity or skip all shakes diet. What carb and fats sources are recommended for any of these diets?
For veggies, would vegetable powder work in your shakes?