I repeated the PLA in acetone experiment with red PLA and pure acetone. Same result, trifurcation after a few minutes:
Here is what happens to an object:
These were identical PLA clothes-pegs, one was dipped in acetone for a few minutes. It fell apart when I tried to pick it out with tongs.
A bit of Googling reveals acetone causes PLA (which is normally amorphous) to become crystalline. That explains why it loses its transparency I think. It also becomes rubbery and crumbly.
Not a very useful result, but it does show that acetone would not be any good for cleaning out a hot end filled with PLA. Also I think people have suggested you could use ABS as support for PLA and dissolve it out with acetone but that plainly will not work either. The opposite works, dissolving the PLA with an alkali.