Alright, I've played around a bit with the powerstroke LPE for testing. A few things I'm noticing:
1. Because powerstroke creates 1 control node in the middle of the path and one at each of the edges, moving the end nodes of the path becomes awkward. You can either move the control node out of the way first or move the node with the keyboard. That's not a problem for me, but I don't know about others.
2. When I select powerstroke on a path and later extend the path with new nodes, the control nodes at the end still remain at their original locations. But, if Powerstroke gets incorporated into the "Shape" drop-down, users will be creating the path as they go, so all the control nodes may be stuck at the start of the path. Any thoughts on this? I guess the powerstroke could be applied only once the user finishes a path. If he still wants to add new nodes after that, he'll have to move the control nodes manually.
3. Cusp line cap style can be either beveled or rounded. No sharp edge option? In fact, rendering is a bit strange when drawing angled segments. If possible the powertroke should have sharp angles in these scenarios too.
4. There are some other rendering issues, like if the control points are dragged too far, or with overlaps, but most users should be able to avoid those scenarios.
5. Mouse-over the control points should show "ctrl+click to create new node" in the description area. It took me a while to figure out that one.
Overall, this tool certainly makes me happy! It's intuitive and easy to use, and it's terrific for drawings and illustration. Rendering issues can be mostly avoided in the most common usage scenarios. I think the only "real" thing missing is 3.: sharp corners along the powerstroke, and easier access.