New feature or functionality

Ability to warp, transform, distort an image or parts of an image with precision

I'd like to see layer masks improved, so I can do things like move or copy them between layers and link or unlink their movement with the parent layer. I'd also like to see improved brush compatibility and be able to apply effects and adjustments ...

I'd like some way for Painter to remember the recent colors I had selected, and provide them for me near the color wheel.

I'd like a function that allows me to use the transparency of a specific layer to mask other layers in my document.

Most modes available in Photoshop are also available in Painter, except the Linear Dodge (Add), which is very useful when painting light on a separate layer. Please implement this mode.

When I work on one or more documents, I'd like Painter to have some way to manage them, such as showing each one in a tab (like a web browser)

Ability to open multiple images in reference image panel, zoom in and out of reference image, preview in greyscale, ability to rotate.

Enable RYB mode so that blending two or more colors, results in more natural looking colors. It would be nice to be able to mix Yellow and Blue and get green or Blue and Red for a purple.

It would be useful to have the possibility to merge the canvas with all the visible layers above it, into a new layer which should appear on top of them.

Ability to flip the quickly flip the document horizontally / vertically to check for mistakes and fine tune.