Thank you for playing! :)
>For innovation there's companies sticking heat cameras and molecular scanners in handsets.
Good on 'em. Those features (which really are using the base phone for it's screen and CPU/GPUasCPU power) might be better as add-on modules, no? Even if your day job is an insulation technician, do you really want o carry the extra bulk when you're in the pub?
>We could do with some decent optical zoom
That will usually add to the bulk of the camera. You could envisage snap-on lenses, or else there is the Nokia 1020 approach which assumes most zoom photography is in the day time and most low light photography is social and wide angle. Apple's approach is reasonable - just add a second camera with a zoom lens. Then there is that project on Kickstarter which uses about a dozen sensors and lenses, and does cunning stuff in software (one gets the idea their end-game is to sell to phone vendors). Then of course is the zoom approach used by Panasonic et al in their 'rugged' cameras: a mirror at 45º is used to increase the distance from lens to sensor. Oh, I nearly forgot - the Samsung cameras with real 10x optical zoom that also happen to be Android phones. Oh oh oh, one more - Sony took their brilliant RX100 camera and pared it down to just the lens and sensor and called it the QX 100, to be paired with Android phones. Dang, neglected those DSLRs with phone controls. So: You have options. (Phones aside, even on dedicated cameras low light performance is usually traded against zoom range)
>and quality audio.
Has been done plenty already. The Sabre DACs from ESS are considered the dogs bollocks, and are in in phones from LG (G2, V10, V20) as well as from one of the recent Chinese upstarts. In time, the DAC could be supplied by Sennheiser et al in their headphones, by Google in their Chromecast Audio, or by Sonos in their speakers, or by Yamaha in their AV receivers etc etc. Some version of the Galaxy S III had Wolfson DACs.
>Project Tango might be a thing.
Maybe, but not for everybody yet - there is no 'killer app' yet for Joe public to justify the RAM requirements and cost of extra sensors, though of course in time those costs will fall to negligible. There might be scope for using Project Tango to sell clothes online ('scan' your body, and let M&S online show you what their shirt looks like on you). Possibly a candidate as a modular 'add-on'
>I'm a fan of any upcoming device that may offer a degree of ruggedness married to some decent specs (not achieved by sticking an iPhone in a rubber sleeve).
But easily achieved by sticking an iPhone in an Otter case. Next!
>Maybe we could do with a different shape that's not so razor-thin that if gives me cramp after holding for a while.
Again, stick it in a case of your choosing. Otter for the building site, fine leather for the ambassador's party. The point is, the slimness of the phone allows you a choice of 3rd party cases.
>Or build in one of those ring things on the back that are trending (yet ridiculous).
You've lost me. Genuinely, I don't know to what you are referring to. The fault is probably mine because I'm not down with the kids.
>What would be truly innovative would be some crazy new battery technology.
Yes, but the market for those (and thus the investment in their development) is not exclusively mobile phones. Maybe LG will develop such a battery, maybe Panasonic, maybe some unheard of university spin-off. We haven't got such wonder batteries yet, but rest assured it is not for want of throwing money at the problem. You can't blame mobile phone vendors for not speccing a technology that doesn't exist yet - it's like saying Toyota isn't being innovative because their cars don't fly and aren't fuelled by banana skins, and whilst they can reach 88Mph they don't travel in time.
>Heck, even stick a solar panel in the back so those of us in sunnier climes can charge up on the windowsill sans cable.
Again, probably best suited to a modular add-on. I mean, if the solar panel was useful for 6 months a year, why would you want to carry the bulk of the device around with you in winter? Efficiency aside, wouldn't you rather the solar panel charge a battery pack, so it can continue to accumulate solar rays when you're actually using the phone? And if you're not using the phone that much, why the hell are you needing to charge it so much? Also, you'd want your solar panel to be bigger than your phone. Because physics.