Grease Pencil Brushes?

Iin Draw mode, Vers. 2.8, using Grease Pencil, is it currently possible to draw or create a stroke that is bold in the middle, but fades, or is soft, on either side of the stroke? Or, is this something that must wait until the final release?

Yes. you can.
Line, Arc, Curve tools have a thickness profile feature.
Brushes have settings that can be influenced by pressure of stylus.
You can modify strength under sculpt mode after drawing the stroke under draw mode.