I'm working on a street system tool for an artist and would like to give them the ability to add any number of curves in Unreal that will eventually become street segments via my HDA.
Is there a way to have an open-ended number of inputs to my HDA? (Specifically curves positioned in Unreal)

Your HDA could promote a multi of object path parm. For example the multi on the Object Merge node. Each of those will become an input in unreal that you could choose Curve Input or whatever.

Thanks Chris!
I'm bummed to reveal the noob I am but how do I create and work with multi params?
I can't find any real docs about them and poking around the HDA type parameters hasn't helped.
If you could point me at any docs I would sure appreciate it.

Just drop down an objectmerge node and drag the “Number of Objects” onto the parm list of your HDA's Type Properties window. This will promote that parm to the HDA interface.

As for docs, I'm not sure. Here's a random tutorial though: https://www.andynicholas.com/?p=639 [www.andynicholas.com]

Awesome, thank you! Never saw that tutorial before either!