For me, support for the Apple Pencil will be the deciding factor. I could care less about the Smart Connector.
I purchased an iPad Air 2 on sale at Christmas time (at a price that was almost too good to pass up on), a month after getting my iPad Pro, because my iPad mini 2 had started acting wonky. In the end, I decided to return it and wait to see if the Air 3 has support for the Pencil. If it does, I'll scarf one up the day they are released. If no Pencil support, I'll wait until the mini actually dies before replacing it.
I purchased an iPad Air 2 on sale at Christmas time (at a price that was almost too good to pass up on), a month after getting my iPad Pro, because my iPad mini 2 had started acting wonky. In the end, I decided to return it and wait to see if the Air 3 has support for the Pencil. If it does, I'll scarf one up the day they are released. If no Pencil support, I'll wait until the mini actually dies before replacing it.