Right now, the playback engine has no knowledge of the "tree structure" at playback time.

For example, if your tree had:

Rush
.....Permanent Waves
.....Moving Pictures
.....Signals
.....Grace Under Pressure

When you play the Rush playlist, it "flattens" that tree before playing it. Once the songs are playing, it doesn't "know" one album from the next, it just knows that there's a flat list of songs where "Tom Sawyer" (Moving Pictures track 1) comes after "Natural Science" (Permanent Waves last track).

So there's no way to do it in the default software without rewriting how it handles the playlist tree.

Programatically, I don't know how a third-party app could possibly hook into the player app to be able to reliably control this.