Will the appx manifest allow you to opt-in to run in the app-container 100% of the time?
Will I as a user be able to force apps to always run in the app-container and restrict its permissions so I can deny internet access etc? Please don't fall into the Android trap here, this is your only chance to give users control over their own machine!
@Joseph Hatfield: Yes, setting WINVER target can break down-level platforms since it changes struct sizes etc, so if you do sizeof(structvarname) in your code, it will break. You could maybe try to #include the COM headers with a different WINVER. Or be careful and only use the size constants like NOTIFYICONDATA_V1_SIZE.
Too bad MS did not opt for a min and max version solution when they moved to the NTDDI defines.