The back accessories are pretty neat. I like the finger loop, and I’m pretty sure they’ve published the files for making your own 3D printed versions of the backplate.
“But hotswappable battery”
Yeah, I guess missing that feature is bit unfortunate, but the reasoning of being able to offer more capacity in the (soft case?) design makes sense. The hardcase of the hotswap battery reduces internal capacity. And it’s still easily replaceable enough when the time does come.

Custom ROMs I’ve already seen mentioned elsewhere, them offering to ship you e/OS/ directly from their store should be proof enough of their commitment.

The “moments” slider is (somewhat) programmable. As alternatives to Moments they offer DND, Flight Mode, Torch, Dark/Light mode, and battery saver.

It may not offer a dual SIM tray, but it does offer dual SIM through the use of eSIMs. Which, not ideal, but it’s there.

The things I personally miss on the FP6 are HD haptics, the basic rumble motor has brought me back in time in a way I would not have preferred. Speaker quality could be better too. As could the cameras, but those were a sacrifice I was prepared to make.

My bigger complaints are about stock Android itself; Samsung offers so many nice tools to customise the phone to your liking. Base Android is so limited by comparison. And Samsung Gallery is just the best.