I am looking for a way to favorite an app I happen to like on Windows Store which I plan to install later (e.g. when I have access to WiFi) or simply have it in my list of favorites, like that in Google Play Store. I didn't find such an option in Windows Store. I am using Windows 10 Mobile build 10.0.10586.11.
Currently there is no "Favorites" feature in the Windows Store. I probably would use the "Share" button so save the app link to a OneNote page or a similar app.
You can also add large apps to the download queue where they should wait for Wifi connection before downloading - not sure what the current threshold in W10M is though.
You should definitely add a feature request in the Windows Feedback app!