I disagree with this implementation. It is very likely that in real use someone would likely try to join upwards of dozens of geometry variants manually (I would disagree with this approach but nevertheless this would end up being a bug report). The implementation should be able to support any number of joins should the user decide to do so. More nodes than the join node will likely need to support this type of variable input as well. This solution needs to be more robust to be used elsewhere.

This implementation has been deprecated. I talked with Hans Goudey. about this and he said, that there should be a new socket type to handle this: Please See https://developer.blender.org/D10067