I wouldn't want to see it purely positionless; I don't think we need five guards.
I'd say perhaps two forwards / centers
Two guards.
One position for either.
Ya, truly positionless there would be some years I'd just hate the results. Using MVP voting for a proxy:
In '94: Hakeem, David Robinson, Pippen, Shaq, and Ewing finished top 5. That would put 4 Centers on your first team and a SF.
In '95: Robinson, Shaq, Karl Malone, Ewing, Olajuwon. 4 Centers and a PF.
In '00: Shaq, Garnett, Mourning, Malone, Duncan. 2 Centers, 2 PF, 1 PF/C.
I kind of feel like things like All-NBA Team, All-Defensive Team should actually have some semblance of a team somebody might actually put out on the court. But of course, on the other hand All-Rookie Team has never worried about positions.
Maybe the NBA should move away from "Teams" and go to individual player rankings, where instead of 1st Team, 2nd Team, 3rd Team, voters rank their Top 3 Centers, Top 3 PFs, Top 3 SFs, etc. They're still recognizing 15 players that way.