@pencilneck Hi! Thank you for taking the time to report your experience with the software along your feedback 
I’m afraid that the vector engine is currently halted so it’s considered a WIP (work in progress), however from a practical standpoint, it is near useless and I could even be as bold to say that is simply broken because of the difficult user experience it provides.
The development team is honestly hyper-aware of this because its nearly a weekly topic, but it is important to note that the developers & contributors are simply volunteers (everyone here is working pro bono) and they work when they can on the features and fixes they want and consider more appropriate. Only in certain situations we gather to prioritize fixes or features that are critical.
As such it has been discussed that the vector engine will be worked on only after the current bitmap engine has been replaced and enhanced (a project which is underway and that you can test by visiting this thread: MyPaint version pre-alpha preview do note that currently the most up to date version for testing is from April 4th, the others you might see are not specific to this feature)
Pencil2D will certainly improve on or completely replace what exists of the vector features, but I’m embarrassed to admit that I don’t really know when this will be able to happen as it doesn’t depend just on one factor.
With all that said, your recommendation on custom tapering is great and will be bookmarked for reference, and actually Pencil2D vectors before version 0.6.0 worked great with pressure sensitivity so at that point a tapering tool was the next logical step, but right now we might need to make everything from scratch as fixing vintage source code, is quite frankly an uphill battle in this particular case.
Thank you for using Pencil2D, we hope to continue to improve this program for the foreseeable future.