Here is a list of tools I think many people would find helpful!
DISCLAIMER: I understand that programming is no easy task, and have a lot of respect for the people who made pencil 2D. So It’s okay if any of these aren’t put in for hardware, software, or other reasons.
With that said, Here is my list!
Ruler: Measurement that would go from where you click, to your cursor. And would show a number of pixels, cm, or inch.
Color Swapper: Much like the fill tool but, Would switch ONE color to another. For example, Clicking on a red circle to turn it blue. Any pixel of the SAME red on that frame would turn blue
Color Remover: Remove every pixel of the clicked color
Color Selector: Select all of ONE color. (similar to a wand tool in other drawing programs)
Shape tool: Square, Circle, Polygon (VERY commonly requested, I know…)
Text Tool: Quick way to add text, Simple font or more, Bold Italic and underlined.
Air brush: Like the one in MS paint
Rotate tool: Rotate whatever is selected
Flip and Mirror Tool: Flip selected vertically and horizontally
These are good ideas; I believe for the rotation and Flip Tools, you can go to “Edit > Selection” to flip the selection, or to rotate you can select it and then hold CTRL and drag it to rotate it.
Some of the others are commonly requested, as you know, but the first four are actually pretty interesting (for those I just use other programs and then just paste it back in)