Based on past behaviour
I'm concerned it will be another 8MP camera. Seriously? (Another reason I'm looking at a Nokia with 20MP, thanks very much.)
My main concern is that the 6 WON'T have a much larger screen. The most reliable rumours have been about pixels and not screen size, at this stage.
It's 4.3" minimum for me or I'm going to Nokia Windows for a while, because Apple just doesn't seem to be getting the message about how far behind they are on screen size.
The other problem might be iOS 8 compatibility. iOS 7 was constantly rebooting on the 64 bit 5S, and it's safe to say, the hardware was known well ahead of time last year. IF the 2 sizes rumours are true, the hardware will be up in the air until the last momentand that looks like another iOS7/5S incompatibility situation in the making.
Apple quality has taken a dive in the last year or two. Too many devices and services now, with not enough people to maintain the quality. Everything is even more rushed than when Jobs was there.
Where services should be improving by now, they're just getting worse. Podcasts got even worse again this week. My iTunes is hanging, crashing, and popping a dialogue every hour (there it goes again) about logging-in to a podcast in my library that finished up in 2009 and wasn't protected when it was active! And last week a podcast appeared on my iPhone called Not Found and not the slightest clue where to look to fix that.
So, not much confidence in Apple software in general at the moment