While reading the thread I thought of something. What if the effects could be applied in a separate mode in which you choose the desired effect from a menu on the side (or wherever) and applies it to the desired note(s) by touching it with the stylus. Draging the stylus over multiple notes would apply the effect to those notes.
Then when the effect is applied it is visualized by a colored bar displayed over the note (the bar is placed behind the note text when going out of effects mode) and the amount of the effect can be changed by holding down on the bars left edge and sliding it right/left to the desired amount. For precision, a number can be displayed while doing so and you could use the D-pad if you only wanted to change small amounts.
It would possibly look something like this
I've always found that applying effects in trackers is tricky business and takes very long to learn how it works, especially since nearly no two trackers use the same effects legend (as far as I know). A more graphical interface would help those (like me) who haven't fully learned the mystical ways of tracker effects.
Does it sound feasible?