I played around a little with the GP brush system. It has its limits, but you can get some nice results with a repeating texture on your stroke if you set the stroke from lines to dots and fiddle around with the brush options like jitter, input samples, opacity…
some of the downsides are that it is quite dependent on the zoom/scale of the drawing. It also generates a lot of points, so applying a simplify modifier might come in handy at a certain point
the blend file is here, contains some other textured brushes as well
I also started a thread to collect nice to know things and resources about the new grease pencil, if anyone would like to join me in my efforts, that would be nice 