Android

Max 4 inch screen, IR blaster, physical keyboard with speed dial settings for buttons, form factor like the Xperia x10 mini pro, headphone jack, cameraless, LED with customisable lights for different notifications, bonus - built in projector, satellite phone capability,

Modular everything. I really wanted Project Ara to come to market.

Phone upgrades.
Battery.. Non lithuim. Flexible and new. []
Flexible screen. Wrist strap or just flexible. []
Fitness/health capabilities. []
Usb 3.1 reversible.. Proper specs [x]
Wireless charging. Using new WiFi microwave to charge phone without mat. Wattup []
Better nfc/Google pay [x]
Smaller screen oled,s than 5.5 []
Better speakers none conduction or ceramic
Encryption []
Bezelless. Screen to screen hole cut out. 2018 []
Solar panel in screen. Sapphire glass. Smudge and germ

This list was created a few years ago.

Some things have been implemented but not all.

Plastic back and a removable/user replaceable battery.

Yeah yeah I know it "feels cheap" but honestly I LIKED when phones were made of more plastic. Now they're heavier and both sides are breakable. Like, the metal backs were fine, but apparently metal backs suck for NFC and wireless charging so instead of giving us some classy Nokia Lumia style plastic they went with glass backs.

Also I keep my phone in a case because otherwise the back is so smooth it shoots off the couch if someone walks across my apartment. It's legit only in the case to add some friction.

Ability to use the screen as a display through the USB port so I can debug a lot of my systems at home without needing to carry a monitor around.

Headphone jack. 5in or less screen size.

Better system font/typeface selection and a way to install new ones. I know it's a petty gripe, but the default android options are few and terrible.

Slide out controller, like the Xperia Play. I've gotten super into (at least the idea of) SBC handheld gaming, and there's just nothing quite like the Xperia Play now. Sure, there's bluetooth controllers, but I'm not a big fan of bluetooth, and the majority of the bluetooth controllers make portability a pain rather than it being a sleek package.

Niche or not, I want an SD card slot that actually fucking works. Like, yes, I can move files to it, but I can't actually install apps to it. There's the "move to SD, but that doesn't matter when the app files are still stored on the internal storage.

Honestly, headphone jacks are number 1.

Then also, FM radios. Most Android phones had them up until a few years ago, when Apple stopped shipping iphones with the feature, to push more people onto iTunes. I'm not a huge radio listener. But having the functionality during an emergency is invaluable. There was a really bad storm in my country a few years ago. Me and my family had no power and no internet for nearly a week. I would listen to my battery powered radio to get weather updates and to find out what the situation was like elsewhere. I don't understand why that same functionality can't be implemented in phones.

Besides that, removable batteries, sim card and SD card slots.

Officially supported rooting! Makes this less complicated.

Does the alert slider counts as a niche feature? Very few brands provides this.

A full physical QWERTY keypad on my 3rd hand Blackberry Bold (in 2013) was the best thing I had seen on a cell phone. I wish full physical QWERTY keyboards would make a comeback.

3D Screen Pico Projector HDMI out Notification LED Removable battery

The first smartphone I owned was the Lobster 700TV, Which as the name suggests had a digital TV receiver built in. The screen was too small to be practical, but I've always liked quirky features like that

One without a damn camera, I swear to God most of the price goes into having "quality cameras" I never end up using.

a decent battery life and a big screen, I bought a pixel 7 pro and am very satisfied.

I loved the IR Blaster on my old Galaxy S4, was really fun to mess with the TV's in public places with it sometimes and was also pretty useful at home as well!

Headphone jack. I've used multiple LG phones before, currently using the LG V60 and seems like Sony is the only way to go in the future, unfortunately.

IR blaster

Foldable display - They are still way too expensive!

Metal case - I just loved the heavy Samsung Omnia metal case. It made it unbreakable and grippy!

Larger, swappable battery. Squeeze for assistant

Today my wish is for an internal pihole instance running on the device.

I enjoyed the squeeze to activate assistant on Pixel 2 XL..just felt right. I even configured it to activate flashlight when I needed a quick light.

I liked the physical toggle for silent mode on iPhones. Flip/slide-out keyboards were also kinda cool

As far as apps though... I really loved having a good programmable remote app on devices with an IR transceiver. The best one was actually on Palm of all things, and you could add custom icons to a layout and then record inputs from your actual remotes to replay.

I've had 3 Motorola's where the charge port stopped working just past warranty. Now I always look for wireless charging.

Keyboard. I want a damn keyboard. I'm a blackberry refugee hiding out on a unihertz titan/titan slim

A swappable battery. I could buy a few batteries and never be out of power. I could replace the battery on an older phone without pretty much having to replace the phone itself.