Allow to sell the universal app only for the phone
Currently a user can buy only a full pack of the universal app.
If someone wants to buy just the desktop app, that is not a huge problem (as price is still right). But if someone doesn't have any use of the desktop app and wants to buy only app for the phone, he would still have to buy whole the pack, which is probably multiple times more expensive than sole phone app would be.
If you think that universal apps are the future, they don't have any future as pay apps on the phone unless this is fixed!
A universal app can be made to target a single device type. If you want to sell the Phone and Desktop apps separately you can do that, only have to manage them as separate apps, with different price, and a different name.