Try posting this question on the CP Forum "Windows API and WinRT/Metro"[^
A Metro app, I am told, can receive a notification a file has changed (it could have been changed by a Win 8 app), and respond to that by reading the file, but, as yet, information about any exchange of data/interaction between Metro and everything-else, beyond file-watch notification is ... missing.
See the question I raised here:[^
] on that Forum I just referred you to, and the responses.
Personally, I find it hard to believe there cannot be a fast, dynamic, method of interchange of whatever between Metro and Win 8 apps, or some equivalent to what we have now with the relationship of .NET and API calls ... but it appears that way now: and, if, in the long run, that turns out to be true, then I will continue to believe that Metro and Win 8 are an example of "schizophrenia" :) (yes, personal bias)