This is a request to add support for dynamic flow control in material editor. Right now it is impossible to get dynamic shader branching using material graph only.
The issue is described in detail in this thead
UE-33876 is the ticket number for this issue, since Issues Tracker went public. Additionally, this post has direct relevance to the problem.
what ever happened to this? UE-33876 is gone…
Apparently it had been removed from issue tracker for not being an issue, but rather a feature request.