Hello James,
Looks really great, closer to that what you want, but not the ending. Caused by my inadequate english I misunderstood some of your statements. After a closer look to your node files I think, the easiest way would be a variable input length for curve groups like in the bundlePts node - like you already mentioned!!!. For a standalone node it is possible, but I don't know if I can integrate it to the existing. I have to check it in the next days.
Nevertheless I think the tests and experiments here helps to find solutions, gives example for people that want exactly such a result and shows what is possible in general.

Thanks and
have a nice day
Karsten