For H/W then the core functions obviously can't live without. Ability to call and message people, take photos, and mobile data. They are the only must haves.
In terms of want to have features but not deal-breakers, then I'm old fashioned I guess. I would like to keep my RGB Notification LED and 3.5mm Headphone Jack and, to a lesser extent, the IR Blaster.
RGB Notification LED: AOD is fine and obviously provides richer information but is not nearly as visible as a good notification led. I guess it depends how much you use your phone. I try not to let the thing control my life and will happily leave it on a desk and do other things. LED is much more useful at these times when I don't have my phone on me. I can easily glance at the phone from a distance and see if I have missed calls, WhatsApp messages, SMS etc depending on the colour and then can decide whether to ignore it or not. With an AOD, at least the ones I have seen, you need to be pretty close to see the notifications. So with no LED I know I would be constantly checking the phone incase I have missed something. That's just me though
Although I agree, a smartwatch would solve this but I really don't need/want one.
3.5mm Headphone Jack: I have a great pair of Sennheiser wired headphones I bought around 4 years ago. They still sound great and are in spotless condition. I can't see any reason why I would need to replace them for the foreseeable future. Not really interested in wireless ones. I don't like using headphones when I'm out and about. But if I did, I could use them both. Nice to have a choice. Also, what happens when the battery dies after the warranty period? Buy another, into the landfill.
Dongles are just a pain. Some work some don't. Quality varies. Easy to lose and damage. Can't charge at the same time as using them at night.
IR Blaster: Ok, this one is really just a nice to have. I use mine maybe just a dozen times a year, but when I need to use it I'm very grateful to have it (for air con when batteries dead, hotel/gym tvs when the remote is missing or broken etc).
That's why I'm stuck with my Xiaomi Mi 5
