Stroke" auto-masking requires too much precisions. You need to click direclty on the stroke to make the brush have an effect. It would be better if the nearest stroke to the cursor position would be detected, similar to selecting.

I can try to improve that.

About Automasking Layers and Materials, IMHO we would need both options: Active Layer/Material and Stroke Layer/Material... I mean, sometimes is good to masking the active layer, but your idea is add a new type to use the layer of the stroke below the cursor...the same for materials, so we will add 2 new modes.

the way it currently behaves in grease pencil forces the user to toggle the auto-masking options for each brush individually

This a known limitation in Gpencil...we haven't a shared settings (global) as you have in mesh sculpt where you have a brush settings, but also a global settings. The same problem you talked about is for size too. We could try to move to a shared place the automasking as you propose.

Adding two more auto-maskign options sounds fine. I just wonder if it makes more sense to use the already existing "Auto-Lock" feature for layers.
The same feature could be introduced for materials as well.

Once there are global auto-masking options I think grease pencil also needs a pie menu to access them. In mesh sculpt mode we use Alt A.
I have an idea how we can make the Alt + A shortcut availbile for grease pencil sculpt mode:

Here are some flow maps showing the issue of the De-/ Select All oeprators in sculpt mode.

This is a visualisation of the current use of the shortcuts. Note that Selecting All and toggling the selection mode off has the same effect.
Meanwhile Deselecting All will lead to the undesireable effect of not being able to do anything.

If we instead use A to toggle the current selection mode we get the same effect within sculpt mode, only faster in just one step.
This also opens up the shortcut Alt A for future global auto-masking.

We could even expand like with mesh sculpt mode by using a pie menu for the A shortcut.
This pie mneu could make any selection operator very acessible like:

• Select All
• Deselect All
• Invert Selection
• Toggle Selection Mode

I have been looking at the code and it's possible to reuse the unified size and strength already in place for Mesh Sculpt brushes. If we reuse this, we could use the same size for all Draw and Sculpt grease pencil brushes. My only concern is that this also will affect on the Mesh Sculpt brush size... I mean, if you change the size of the brush in GPerncil Sculpt, when you use a Mesh Sculpt brush, you will get the same size. Same for strength.

About the masking options, if we start using unified settings, we could move the actual masking options to the unified structure. Will we have to keep the masking at the Brush level, or can we consider these options "global"?

Here's my view on the "Unfiied" setting for brushes: We should make this setting eventually as mode specific as possible.
Meaning that each mode in each object type has its own unified value for settings.

This will for example ensure a unified size or strenght among different brushes within Draw mode, but in a different unfiied size & strenght for Weight painting.
Each mode has a very different requirement for these settings, so it makes sense to keep them independent.

This goes against the current design so we should discuss this in more detail.
@Joseph Eagar (joeedh) also had interest in adressing Unified setting issues, so he might be willing to share his take on the issues or help out.

For auto-masking specifically I'd still prefer we also include global toggles that are not part of the brush settings.
IMO that would be more useful and consistent.

If we decide to split the unified settings for Grease Pencil, then automasking is not a problem. If we decide to reuse existing struct, then we can add the automasking in this struct too, but will not be visible in any non GPencil brush or we can put in a different place and don't use the unified struct for automasking.

In both cases, automasking would be a global toggle option.

To not blocking this task, we can start moving automasking to a shared place and make it global. Actually, we have already a global setting for all sculpt gpencil brushes, so we can move the automasking there. After moving in a patch, the next patch is add new automasking modes.

Later, we can follow with the unified size and strength, but this need more discussions because it can affect other areas of Blender.