By using the plugin PictureRegion I can add a drawing with a pen tablet.
How can I erase part of my drawing?
Will this be included in a future update?

There is no way to edit picture regions except creating black pixels with the pen.
For really editable images you can use the image region. There is a section on how to do this in the interactive tutorial or in the handbook.
For annotation of images it is best to use superimposed text or math regions.

Wrote

By using the plugin PictureRegion I can add a drawing with a pen tablet.
How can I erase part of my drawing?
Will this be included in a future update?

1. There are plenty of freeware CAD drawing.
Some can save the creation AutoCad and read back 123456789 km away.
2. Picture tool is on shot draw for kids, don't like ... redo.
3. Insert picture from file 1/1 ... zoom by aspect ratio,
of exceptional quality up to zoom 2. Zoom by handles.
Calipers is a freeware tool.
4. Paint does what you are asking for.