Thank you so much for this! It works very well.
My summary of your algorithm: Pipe with meshpipe, then rescale the cross section curves with a factor based on their position along the input curve.
Find below an example where your algorithm is applied to a little sample tree. I restructured your definition in order to understand it better. And I did some changes to the algorithm. Most notably, I changed the way cross section curves are detected based on them being closed curves. I have no closed curves in my input curves. I also made it work for a list of input curves instead of just one.
2025-02-22+08_polyline_pipe.gh (34.5 KB)
Here the application to a big, and not very realistic, tree:
2025-02-22+08_polyline_pipe_big.gh (30.7 KB)
This is interesting and made me come up with an alternative algorithm. Instead of tapering pipes, it varies the amount of pipes. Each pipe has the same diameter. Thus the piping operation can be done in one go. The look might work for my use case, which is modeling banyan trees.
2025-02-22+08_polyline_pipe_many.gh (19.1 KB)
And for a big tree:
2025-02-22+08_polyline_pipe_big_many.gh (24.8 KB)