Their naming makes perfect sense I'd say.
The lower is number, the more advanced and expensive the model is.
Xperia 0 - most expensive and advanced model. 5K display with a wide array of cameras.
Xperia 1 - 4K display and triple camera. Perhaps some distinctive differencies.
Xperia 3 - 4K or FHD model with triple camera, new form factor (arc) and compact dimensions.
Xperia 5 - smaller brother of Xperia 1 with FHD display and classic form factor.
Xperia 8 - model with midrange camera and processor, but packed with flagship materials, water resistance, etc.
Xperia 9 - former Xperia 10 plus.
Xperia 10 - well... Xperia 10. :P
And Xperia 11 (?) or L3.
Decimal numbers like .1, .2 and so long mean generation of the device.
So, for example, Xperia 1 means 1st generation, and next year model will be Xperia 1.1
This naming scheme sounds pretty clear to me.