"Breakthrough"? Let me guess:
1.microSD card slot,
3.great battery capacity,
4.(privacy) settings that don't get changed automatically without informing the user about anything,
5.cameras that don't turn themselves on automatically without notification?
That would definitely be amazing to begin with. Innovation? Curved screens (hint, hint, SGS6 Edge), or anything to make that phone stand on its own and not be "just another piece of plastic no effing different from the rest of the pack"?
Oh yes, that would be great, but who do you expect to bring that? Microsoft? The [unt behind Windows 10 (a.k.a. the Spy Operating System)?
How about phone with an Intel chip and x86 copy of Windows 10 rather than the ARM version and continuum being a dual screen windows rather than something too clever that doesn't actually work for most people.
Too little too late? I was a 920 guy, now a 1520 but I just bought my wife an iPhone and may follow suit.
MS has failed in the phone biz. And of all the things to kill it? No app support or something that deters companies from making WP apps. Who knows?
Breakthrough? My old xt910 (razr) from 2011 has HDMI out and has a desktop suite (webtop) that has a desktop, mouse and keyboard (wireless or usb) with a pre-installed office suite and all the other apps available in the play store. And it works well.