[Cmart]

Are you wanting the start/end points of lines to be round versus square? That's not a difficult thing to add, I would just need to add a new setting to the shapes dropdown as well as a new entry on the radial menu for it. I think the bigger issue is that whatever label I use for it, I won't have a translation. I suppose I could just reuse the old "Draw Mode" label, but next to the label, I would show two icons as toggles: a picture of a short line with rounded end points, and a picture of a line with square end points.

How about a checkbox to the right of "dashed" that says "rounded"?

What staff options are you looking for exactly? It was a lot of work to even set up the piano staff. I had to design vector graphics for the start of the staff, the middle of the staff, the end of the staff with one line, and the end of the staff with two lines. It took a considerable amount of code as well to handle creating those (as well as the touch interactions to create them). I'm okay with adding support for more things, but it's not going to be incredibly high on the priority list due to the complexity involved. While I do want to support some basic editing capabilities, MobileSheets is not really a composition app, so unless adding more kinds of staves will be beneficial to a lot of users, I need to focus on other things first. As a side note, I'm not sure if you are aware, but there are multiple things you can do with the piano staff:

1) You drag first to position the piano staff, wait for a half second once it's placed
2) You can drag up or down to scale the piano staff up or down as needed.
3) Drag right to specify the length of the piano staff. Once you stop, if you release, it will create it as is. If you wait for a second, it will use an end with a single line. If you wait another second, it will use an end with a double line.

I had no idea it was so much work behind. Don't bother then.
Maybe just a empty five line staff when or if you get the time. I use this sometimes to write in an ornament or improvisation. I will try to add this as a custom stamp, that might work right?