I want to create some extended Binding-Markup-Extension, which behaves just like a normal WPF-Binding but does some things more (use different defaults, maybe add some behavior,
Actually it's not possible in current versions of R# and, unfortunately, still be missing feature of upcoming R# 6.1 release.
This feature requires a lot of infrastructure changes, but it's on our list and definitely will be implemented in R# 7. Seems like [CustomBindingMarkup] and [BindingPath] (for path constructor parameter and the Path property) attributes will be introduced.
We really apologize for any inconvenience.