7 years updates plus 2 battery swaps will take a flagship phone right to the edge of how long you'd want to use it anyway.
I think, 7 years would be amazing, but also good enough. Or to put it differently, after 7 years you get into heavy diminishing returns, since almost all users will be moving on/have severely broken their phone before that.
I've had most of my phones until they where 5-6 years old (I used to buy used, so I had older phones even though I didn't have them for quite that long). After that time, they usually fall apart anyway. (Two of my phones developed frequent random reboots around that time, one wore through the cable connecting both halves of the slider, and one killed died when I tried replacing the battery and accidentally cut through the screen cable).
I think you hit the nail on the head with diminishing returns. I'm usually on a 5-6 year usage period too. I can understand the battery swap helping out but my last few phones have felt so sluggish after 4+ years so I start looking at new phones around year 5. I have a Pixel 7 now and I'm going to wait until end of support and then we'll see what the offerings are then!
I was going to post something dismissive about an air-gapped phone being pretty useless, then I remembered I have an old Xperia Play which I repurposed as a dedicated emulator
battery swap helps a lot with sluggish phones if a factory reset doesnt help, phones will supposedly throttle down to save battery when it starts getting bad
No not the Pixel 8 otherwise it would have a back that you can open. Maybe the Pixel 9 but not likely, but definitely the Pixel 10 because the mandate kicks in somewhere in 2026 and the Pixel 10 would be coming out late 2025 so, that one is the most likely to have a replaceable battery. I have a Pixel 7 currently so I can wait til the Pixel 10