Hello there.
Since the creation of ArtRage it's developers were aiming for a program that's close to real-life painting, with some cool features that are impossible to do in real life (layers, selection, etc.).
But with appearing of Ink Pen many started asking developers to add a features that Paint Tool SAI have, like vector layers, ability to change stroke's width, length, add/delete Control Points, etc. I saw just one or two responses from Ambient Design team on this, that ArtRage is aimed for real-life-likeness, and those features could ruin the program's natural feel and friendly interface (hard to disagree).

So, how about creating a side-project, that's aimed for easing life to those who draw comics, manga/anime, do simple inking and other things? I don't think that it's so hard, it might be even easier. For example, you can drop out the Lighting and Bump features, because they're not needed at comic-drawing. Also a huge plus for program's speed. You can get rid of some tools that are not needed (Chalk, Crayon, Paint Tube, Glitter, Paint Roller - those can be easily replaced/imitated with Sticker Spray).

What should be added?
More blending tools (with ArtRage's Knife I can't get the same results as with PaintTool SAI's blenders) for comfortable drawing of hair, clothes, etc.
More Inking and Vectoring features. Like described above - drawing lines with Control Points, dragging them, making lines thinner, changing color, etc.
Better Presets management. All the stuff that's been suggested for ArtRage earlier (a panel with favorite presets, switching between them with a shortcuts and other)
Textured erasing (probably as Sticker Spray's or any other tool's option?).

What should be left as it is?
Textures.
Playback. One of the reasons for openCanvas popularity is this feature.
Adjusting Colors.

Also a compatibility between ArtRage and this project-fork would be great. In one you draw a character, in other you finish a background.
The price is for a team to decide.

And what about the competitiveness of this program... This is all about how it's done. If it will have a better interface than openCanvas (I personally don't like it), will be able to do more cool stuff than Paint Tool SAI (admit it, this program is OLD) and will be as quick as they are, then...

Maybe there's more to do, I just described what came into my mind first.
I hope this idea will be noticed.
Remember that PT SAI haven't been updated since 2005 and it's still very popular... If Ambient Design would just try to create something better, it could be a great success and a big joy for us.

P.S. Yet another thing to say. I know that only a few people are developing ArtRage, and making a side-project can be hard, so I will understand if Ambient Design will reject this idea. Then I'll just wait for ArtRage 4.