OPL4 wave editor for GFX9000

Now that this tool is out, it might be interesting discussing its future. On #msx Marcel Delorme (msd) already announced he might support the Meridian Tone Format (the format Michiel de Vries' MIDI/OPL4 tracker/sequencer uses for samples). What do you think about this graphical wave editor and what features would you like to see?