I notice that different software has different ways of dealing with inking and making it easier. Artrage applies smoothing to a stroke after it's made. Mypaint(slow position tracking) and some other software (paint tool sai, zbrush(lazymouse)) allows you to slow down your stroke as you make it. I find that the slow position tracking approach is more predictable and easy to control, but takes a bit more patience when you ink.
So that is the biggest feature that I would love to have in any future version. Slow position tracking! Let me know if it already has it, i might be wrong.

Here are some tools that are rare, and in fact selling points of Illuststudio!!

Common problems when inking:
-your stroke overshoots another stroke, creating a cross. That creates work for later to clean the crossed parts of strokes. This gets tricky in dense areas where you end up damaging previous successful strokes.
-your stroke doesnt reach the other stroke, leaving a tiny annoying gap- that forces you to go and carefully fill it with more strokes.
- your stroke's thickness is not good at the end or the middle, but its too late to fix. You end up making more strokes over your old one, but the new ones are not snapped over it, so they are not perfectly covering its middle.

The tools are perticularily useful for inking sessions.

Crossed line eraser tool.
Their eraser lets you erase the area of a strokes that has "crossed" another stroke. This happens often when you ink something. Your strokes cross each other- which then forces you to go back and clean up where they have crossed.
The erase tool in illust studio lets you loosely lasso the crossed-over section, and it automatically figures out the part of the stroke that needs to be cleaned and cleans it for you.
Its a one step process where your lasso only needs to touch the stroke, the tool then automatically figures out where its crossing over other pixels on an angle and deletes the overshoot line for you.

*Fill stroke gaps-
Like the tool above, this one lets you lasso a gap between two strokes. For as long as your lass touched the end of stroke A and the end of stroke B, the tool looks at their thickness and automagically creates a new straight stroke between them. This is a one step process, which makes this tool ultra fast.

*Thicken stroke brush
A brush tool that is used to thicken line strokes by painting over them. Whats neat about it is that the stylus strokes you make with it are being anchored/constrained to the stroke that you are thickening by painting over it. It thickens the part of the target stroke depending on the pressure you apply. That lets easily adjust your inking's thickness- reduce or increase it without the need to deal with clicking on things.

Pixel snapping
Even if you're not interested in the tools above, think about the possibilities of having pixel constraining, not only alpha locking. If we could snap our new stylus stroke to a stroke from before, we can potentially thicken it or delete crossed (overshoot) sections of strokes without damaging other strokes and without leaving messy areas where two strokes are not overlapping well enough..

So I am presenting these problems because artrage has an amazing track record of offering new brilliantly simple yet effective new tools that tackle old problems. It would be interesting to see how inking could be tackled without having to go with full fledged vector node based approach