Paintstormstudio.com

In some sort of order of priority.

A liquefy tool. Many great digital painters I follow use this, mostly to tweak eyes and faces before they begin on their final few detail passes, for instance Stjepan Sejic and Sakimi Chan.

Layer effects like dropshadow, stroke, and emboss. Stjepan Sejic uses these, especially the emboss one to add incredible detail when he's scales and metal bits. Examples: https://youtu.be/qnyfD3tIDeU?t=5m45s

A "Blend If" function as well, for layer effects, so you can do stuff like multiply red into a layer, but only into the darker areas, or whatever. As far as I know, Photoshop is the only program that does this. Admittedly it's a niche feature, but I've found a use for it. https://youtu.be/3GKDBXrpV8s?t=2m5s

I guess I'd eventually need a Text tool as well, and maybe some way to manage color palettes, but that stuff is lower priority.

A liquefy tool.

Already realized - Menu-Filters-Warp

A "Blend If" function as well

Nice feature but in photoshop it works without any smoothnes, what's why it's usually ussless. Anyway in Paintstorm you can select color range by the brighness and smoothit if needed, after that - create mask.

Excellent! I'll check out the warp.

The Blend If is a nice to have feature. I color my comics in an odd way. Without going in to all the detail, basically I do graytone shading, then a layer set to "color" blending mode overtop. This is fairly fast but it means that the colors are monochromatic. Skin is the same hue whether it's light or dark. I'd like to be able to have a Blend If layer above it that adds red into the darker areas, for example, to create warm shadows, and another Blend If layer that creates cool highlights, or vice versa. That way the layer itself could be set to soft light or overlay or just another color layer and I'd have tons of control over it, and it would apply in real time. Doing it as you suggest after the whole page is done is possible, but that would be static and I find the need to make tweaks even after I think I'm done a lot of the time.

Anyway, that's my use case for it.