I had a Tandy 1000 back in the 80s. I think I got it in '88.
It had MS DOS, but it also had this special Tandy GUI which was like a low-res version of windows.
Anyway, back on topic...
Squall, this is a mock-up of what I envision the UI to look like:

The "song info" is a few commands that are always at the beginning of track 1.
Track info, with the exception of the track number, appears at the beginning of every track.
Aside from loops and GoTos, that would really be all the commands needed, as pretty much everything else doesn't really do anything as far as I can tell, or at least not anything useful.
I imagine the track # to be a drop-down box, where the user selects a track, and the program changes what's being displayed as appropriate.
In a perfect world, "view as" would also be a drop-down, and the user could select anything between 1/64 and 1.
The red bars represent notes being played on the track, and their length represents the duration of each note. Empty space would be automatically filled by rests of the appropriate duration.
The viewable field would be one octave, but the user would be able to scroll up or down into different octaves (and the program would insert octave up/octavbe down commands as needed).
Somehow notation would need to be available for loop points. I don't know exactly what that would look like - maybe a blue bar marking the beginning of a loop and a green marking the end? But there would also have to be a way of telling the program how many times to loop (as this is done with every loop point).
The GoTos would also require some figuring out. Since they really are used primarily to determine if the track repreats or not, I guess there could be another box in track info that says "Repeat to" and then the user enters a measure and beat into the field, leaving it blank for "no repeat."
I don't know... Does that seem like something that could be done?