Thank you so much for doing this. I am clearly still learning this stuff!
The fact that you are casually taking a SubD output and feeding it straight into a Brep Join and a Brep Edges component is the part that I find bewildering, as a relative beginner. Sometimes such things are outrageous coercions, that just work, and sometimes perhaps a SubD really is just a Brep surface. No way to find out but to try it! This is a huge conceptual mountain to climb.
I wish there was a way to select a component output and then have the view of available components change the colour of those that would accept the output as an input. Having them change colour to red after the fact is useful, but being able to see what might work in advance would be a good learning tool. Perhaps invalid links should not even be supported, and would refuse to link?
I still think that it would be natural for MultiPipe to provide a mechanism to cap ends, as the old Brep Pipe does. But I will keep your recipe for the future.