AdDuplex is spotting a Lumia device with a 5-inch 720p HD display. It's a RM-1150/RM-1152/RM-1154/RM-1156 and that's all the information about the device we have.
But it is safe to say this is a mid-range device, could be the Lumia 750 or a Lumia 850? Hopefully we will find out on Oct. 6th.
I uploaded a few photos of an unknown Lumia device that got leaked (courtesy @szleaks) a while ago, so maybe this is that device in question? Just an educated guess.
But it would be nice if we got this device launched along with the Lumia 950/950XL.
Microsoft is expected to announce a full range of Lumia devices (from high end to low end) on Oct. 6th.