Holding shift + drag to clone an object is very handy. But we always get this intrusive dialog about (copy, instance,reference, number of copys) that means a double click. Its good to have this options at hand, but when you are copying individual objects on specific places can be frustrating.
Proposition:
1- Have an option on the clone dialog to dont appear this dialog anymore for the selected object or his clones. (so if we select reference and this option, as long as we are shift+drag this object or his references the dialog will not pop up anymore, and we will be creating references).
2-shift+drag will create a popup, but shift+control+drag will just do an instance without any dialog popup.