Not sure if it better to comment here or in D15903 but I have one small wish.
Wish for pixel and maybe smudge brush engine settings. Move the Color setting category (Darken\Mix\Hue\Saturation\Value\etc) to the bottom of settings list. These color options very rarely used but take some space.
Also I think I'll be a little more logical.

I really like that mockup! Some thoughts:

@scottpetrovic @razvanr yes, auto spacing hurts performance on big brushes . Auto spacing is bad, we shouldn't use it without good reason.

I tested brushes and noticed some of them have wrong brush tip or tip settings for masking brushes. These are fixed now. And I saved all names and icons (except clone brush, it have new icon and tip, scott will have to make one more name :P).
I also changed some presets to something better in my opinion.
Tips "chisel_knife" and "chalk_round_hard" changed to blurried versions, they makes better results.
I'll probably play with brushes more and add some feedback on other presets.

In T7424#123350, @scottpetrovic wrote:

1. 45tilt1 and 35tilt3. The mask brush size is smaller than the default brush size so it gets scaled up and doesn't look very good by default

I made some new brush presets with masking feature. Plus some tips and one texture.
It will need better names and icons (as usual :) and Lod threshold tweaks.

In T7424#120674, @scottpetrovic wrote:

2. I can check out the distort brushes. I know for the move tool, if we make it only slight, it is more of a "nudge" than a "move. I would have to play around with you setting recommendation though to judge better

As an artist I'd say slight effect is more useful in work.

4. How does a marker work? I guess it could have slightly opacity differences. When I tested it out it felt like using a marker so I added it. That was about as far as my mind went with it.

If I remember correctly problem with marker is that it uses "build up" mode, change it to Wash and it will be fine.

I made new brush to replace "Clone_Tool_Textured". There is example painting I made with this brush: https://lut.im/YStZMf32yZ/bRpAVZ3OB3MKhcfq.jpg

I tested branch and new set definitely looks good. I have some opinions and questions though.

I made a bundle with all brush tips I'd take to default pack, some of them are mine, some from krita.

In T7424#118562, @woltherav wrote:

All color dodge does that makes it feel more "correct" is increase the difference between the channels which leads to more saturated results.

In T7424#118543, @woltherav wrote:

I would prefer to keep the blur brush as it is the only one that can provide proper blurring in 8bit.

People actually use Blur brush for blending? I think main problem is that blur radius is always 10px, if It would be related to brush size it will be pretty much same as sai blur brush.

Addition blending mode is also preferable to color-dodge as it actually works properly in the floating point spaces.

Just tested in 16 bit float. I see some color artifacts with hard overlay and addition, color dodge works fine. I suggest color dodge and hard overlay because they gives more correct result when used to add light to painting.

Yeah, I'm not good at naming.

Turned out I cannot upload files to Preset and tips table so I made zip file with brushes and tips for them. Most of them have weird names and icons :|

About icons.
Current icons have one advantage - they looks really nice. But looking nice isn't the main purpose of icons, icon should show user what to expect from this particular brush.

In T7424#117547, @scottpetrovic wrote:

@radianart - I am sure we can eventually add stacked brush presets...but that isn't done yet. We shouldn't worry about that right now. We can add those whenever that feature is added.

Then we will have repetitive and redundant presets again. Point is stacked brushes can replace some animated brushes and be much better. If stacked brushes will be implemented relatively soon I'd prefer to have better presets.

Proposal:
Make Krita open by default a tag "Basic". This tag contains the future brush kit we are speaking here, friendly, clean for general usage...

This doesn't solve the problem of too many useless presets.
I don't think we need brushes for everything by default. Just 2 or 3 dozen of good brushes what will be enough for 80% cases. You need many different textured brushes? - welcome to share.krita.

4. textured strokes
5. mixing strokes

I experiencing crashes with textured brushes. Noticed on brush like here https://phabricator.kde.org/T7052 but it happens with other too. It need a couple minutes of painting to get the crush, simply brushes seems to be more stable but I got crashes with them too. Even just hard round with texture can crash.

Some bristle comments:

Brush tips that isn't useful from my opinion:

Updated diff for multithreaded update. Also fixed problem with default value.

Pushed

Some more thoughts from forum:

Little change to make code more logical.

Some thoughts about editor (+picture):

Idea: fill path with .kra file ()path and name with .kra file name + layer name by default.
like path - "C:\myart\october" and name - "the_best_painting - background.kra" (png?)

Updated ui to make feature more noticeable.

I think he mean to apply Brightness and Contrast to texture preview on this texture chooser widget.

I feel auto fps make it pretty smooth on low-mid brush size but it becomes low fps too early.
Brush - Block_textured_1, low pressure (because it high pressure makes spacing lower).
Size 200px - 20 fps
260px - around 15 fps
365 - very 11 fps but brush still very fast
506 - still pretty fast
650 - it noticeable slower

I like this editor design more. And now it shows big brushes much better. But strokes still don't fit into view very well. Also I'd prefer bigger preview (I see space between brush settings and preview borders but I'm not sure it's possible to use).

I checked out preview branch, great work! But I see 2 issues:

In D8030#150429, @rempt wrote:

I'm all for it, but the sliders should be as wide as the other sliders in the widget.

About placement, I see 5 variants for now:

Hard Overlay

I'm agree with most of the points above but I have a couple more wishes:

1. Ability to turn ref picture grayscale.
2. Hide UI button, which will hide all buttons\slider on the docker itself. Except little "+" button on the corner which will bring UI back.
3. "Navigation sync" (or navigation link). All navigation moves (pan, zoom, mirror, rotation) done to canvas also applies to ref picture too. The idea is to make it relative, like "zoom in two steps" will 50% -> 100% for painting and 100% ->200% for ref, same for pan. This way ref picture and painting don't needs to be same size or aspect ratio. One of usecases: few portrait ref pictures and one .kra file, sync and paint one portrait, unsync, change ref and pan to other area of document, repeat.

A bunch of ideas about resources management from point of view of brush creator. It's not about some particular resources or UI but mostly about work logic. I hope you'll find something useful and sorry for my English again.