I’ll continue to say that it is quite impossible. For Android Devices, maybe a few are listed, for iOS, they’re identifiers are secure. I’m looking forward for a test site from you where I can log in from all my 27 test devices and that will identify them. I’m only telling your their brands. Nokia, HTC, Samsung, Apple, MI. Now, please, convince me that it’s impossible. 
HSC’s serve on different parameters. And Google Analytics searches for something completely different to identify the devices, and as a notice, Analytics can only detect a few android devices, usually major players, never low end devices, and considering most users that browse a mobile device may NOT have 800$ to purchase the latest and greatest smartphone you’re leaving out HUGE gap in “unknown devices”.
But I might be wrong. I’ve just been doing mobile custom mobile websites for about 10 years, with every possible tracker you can think of for customers. Who knows!