For starters, you should be able to select multiple items in there, it's very annoying when I want to delete a bunch of samples or patterns at once and I have to go one at a time instead of just box selecting and pressing delete all at once, might be even faster than using the cleanup menu in certain circumstances! Even if box selecting isn't possible, it's very annoying when I instinctively shift or ctrl click to select multiple items on there only to unselect the first thing I clicked, so that could be added instead

In the same vein as that, being able to drag samples or instruments would make working a lot faster, so instead of having to open the sample tab in one song, copying, going to the other song, and pasting, you could just grab the sample and bring it over, not to mention if you want to use multiple from a sample or instrument bank you could just select them and drag them all across instead of pasting one at a time.

Finally, being able to "add" patterns into the hierarchy should probably be added, it seems so weird that you can Edit, Delete, Set, Rename, but not make a new one.