Luckily for me, it seems my most wanted featurer are already the ones being worked on! (infinite canvas, faster performance, grayscale mask) I've been testing Krita's various features these past few weeks, so here's a list of additional features I'd like to see (in no particular order save for the first one):

1. Linked masks 2. Vector masks

Whoops, I finally realized how that "lock alpha" feature works. And that it works with vectors. That takes care of those. Sorry!

3. Transform perspective from dragging corners individually

Scenario: a user creates a 2D poster. He wants to apply it to an exact section on the side of a wall.

Ideally the user would want to achieve that by dragging each corner of the poster onto the corresponding spot. Currently Krita starts flipping the whole plane when you drag a corner, which is less easy to control.

4. Better color dynamics 5. Easy gradient editor

Nevermind, finally figured out how these work. Whoops!

6. Save brush palettes

I think 8 brushes in the brush palette is quite enough for any given section of a picture you're working at, but on the other hand, what's useful is being able to save and load different brush palettes. For example:
- Different palettes for different styles
- One for drawing faces
- One for different types of vegetation
- One for rocks and mountains
- etc.

7. Brush dynamics settings

There are two more things I'd like to have for curves:
- A "Reverse curve" checkbox. Basically, sometimes the curve is the opposite of what you want (for example, for airbrush effects, you want the brush to be smaller when you're drawing faster). Reversing that curve manually is a pain though.
- Saving brush curve settings. This is still independent of the above checkbox though, since the above checkbox would be a quite common usage you'd want to access quickly.

Oh by the way, please change "fuzzy" to "random", "fuzzy" makes you think of a brush with high softness. D:

8. Group level transforms

Right now if you select a group and use the move tool, it moves all the layer in the group, which is awesome. Could it be also possible to use the free transform tool simultaneously on all elements of a group?

Anyway, I'm sure the devs have their hands full for the next few months already with the current features they're working on. These are just additional features that I think would be useful eventually.

4: You need to enable one of the color options to use the gradient. They defined how the gradient colors are used.

Eh? ... It does work! How embarrassing, in the end, it turned out that half the things I wanted were already there.
It seems I won't have to wait until Krita 2.6 to make a second tutorial, I have more than enough material.