... or at least link-in nodes.
As part of my system design I distribute several useful "events" via link nodes, such as system startup, regular timestamps, email received etc. In many cases, particularly with the startup event, these are fed into subflows, and while tidying up my flows I realised it would be neater if the incoming links were inside the subflow, to reduce clutter and save checking the incoming message.
I've not looked into the code, but I realise there are likely good reasons why link nodes aren't allowed in subflows, such as the inability to specify different connections on a per-instance basis. However, if it was limited to a "static" or "const" connection, then it might make it simpler to implement.
It's probably not a high priority, but I'd be interested to hear any thoughts on the possibility of implementing this.