Let's say, I have two SIM cards, the first one has an unlimited but slow 3G internet connection, the other SIM has a very fast LTE Internet connection with limited data volume. So I would use the first SIM card for all apps, downloads, web surfing, app updates, music streaming, data synchronisation like Dropbox and Google Drive etc. But for Skype/WhatsApp video calls and HD video streaming I would prefer to use the second sim card with LTE. Is that possible on Android?
If it is inpossible, probably another scenario will work somehow: if I start Skype/Netflix, all background internet connections should be stopped and the second sim must be activated for internet connections.
If there is no app for that yet, but it is possible to do so programmatically without rooting, that would work, too.