I'm trying to create a Python Panel that provides me with a custom editor based on node selection. However, I can't find a good way of detecting when selection has changed, or what the current/last selected node is.

I see that there are callbacks that I can add on a per-node basis, but I feel like there is a feature that works more globally, like how all the native editors work, and I can't seem to find how to hook into it… (ie the Parameters panel, which updates based on node selection).

I haven't used it, but have you seen hou.ui.addSelectionCallback(). It sounds like what you're after.