A few months ago I released a visual studio extension, that provides autocomplete if you edit office ribbon files. The extension is open source, and published on GitHub.
By now, it proved to be more of less functional and even some issues with Office 2016 icons were fixed thanks to the user feedback! 🙂
What it can do for you – it can assist you if you edit the XML files to define interface for your extensions in the Visual Studio editor.
The code is based on famous glyphfriend extension (if you don’t use it yet – you should start, it’s great). Initially there was a plan to merge this part into that extension, but it proved to be quite heavy with all those 5000 office icons, so it is now separate thing.