Now, what do we mean by "proper"? In a world where the majority of dual SIM devices allow you to either use two SIMs or a SIM card and a microSD one at the same time, the aforementioned Sony devices above will boast two SIM slots and a dedicated microSD one, allowing you to enjoy the services of two carriers and expanded storage at the same time.
That's definitely not the first time Sony does this: many previous Xperia devices have been available in such Dual SIM editions, most notably the Xperia Z5, Xperia X Performance, Xperia XA, and others.
We have no idea when the "Dual" version of the XZ Premium, XA1, and XA1 Ultra will be hitting the streets; we have no idea what markets these will be arriving in, but as usual, we expect Sony to release those devices across the developing markets and skip the States. We'll let you know if we know more!