For me, I don't think the pleasure of owning a slim and light phone, is worth the misery and annoyance of every day having my battery poop out in the evening which is when one needs of the most. The thing that frustrates me, is that a 20 to 25% larger battery would only add about 15 or 20 g to my phone.
Placement of power button.
For me most of the time when I touch my phone, it is lying face up on a table or chair arm, or my lap. Having a power/home button which point upwards, like the Apple or Samsung phones, I find really convenient and easy-to-use. It is particularly useful on tablets as well. It also means, your fingers are instantly near the menu and back button.
Okay this suggestion is a bit out there, but I don't think it would be a bad idea to have a capacitive strip along the side or top of the phone, facing the front, to give instant volume control. YouTube particularly is always a different volumes and I find fiddling with the side volume controls, or drop-down menus just not exactly user-friendly.
How much memory do you need? Answer = however much you want, probably a lot and very reasonably priced with the option to use your own microSD card. The fixed amount of memory in some phones, in my view is a straight off a moneymaking scam. What's more I can't even buy the amount of memory that I want usually. The Moto G comes in an 8 and 16 gig model I know it's a budget phone, but I'm used to 70 gigs thank you very much.
I like having a removable battery, I love the idea that in a crisis or and extreme busyness I could just slap another battery in and keep going. But also I know that lithium batteries have a limited lifespan. And I don't want the worry of a future large expense of the battery fails.
Getting rid of hard buttons, in favour of in app menus.
I find it more ergonomic to use capacitive buttons down at the bottom of the phone than reaching up to the top corners, because that's where my fingers are. I'm talking to you HTC.
Full power phone with a smaller screen size.
Large screens a great for web browsing and films. But I've downsized to 4.3 inch screen because as a phone fanatic I find it more ergonomic when doing a lot of texting and other stuff. There is no full power or full featured android phone in this screen size. I really wish there was.
I would really appreciate it, if the phone companies would focus on features and phone design that really care for the consumer, with particular attention to ergonomics, based around how our hands are designed, so we don't have to constantly reach all round the phone, giving ourselves RSI in the process. Instead of going for style and slickness and trying to score points against other manufacturers by shaving off millimetres. There is only one manufacturer which comes close to giving me most of the things I want, that is hardly consumer heaven. I know it's a fairly undeveloped market, but I wish things would hurry up and anyone could get whatever phone they wanted with whatever features they wanted.