Yes, this has been discussed.
No, the feature does not yet exist, although selecting a given preset is very easy with the 2.0 software (it's two keystrokes on the Rio remote control: Hold "Equalizer" then press the preset number).
I thought about it and maintaining multiple EQ presets for given groups of songs is a lot of work when you re-EQ your car. Very unwieldy. What we really need is something where you can say "Bass +2db" or "Treble -3db" for a given song.
Applying this to a playlist is a bad idea but group-selecting songs within a playlist (or within the search results screen in emplode or Jemplode) and applying the setting globally to all songs within that playlist would work well.
Stay tuned, Genixia and I are talking already.