We added the Pre-Defined Parameters RootInstanceName and ParentInstanceName in 8.1.13 for these types of relationships, so hopefully one of those can be used to get what you need.
The Customs and Parameters syntax is something I will discuss with the team. I can see how it could be useful.
Yes, the {[.]}…/Parameters.xxxx syntax is already there, my wording was just a bit off. It is considered by the system to be a folder which is why it works how it does. The custom props one might be a bit cumbersome to add because they aren’t separated out of the definition like parameters. We will discuss other options as well just to try and make it easier to find a solution to this type of situation as there is a clear problem that we should try and make better.