A larger capacity sealed/embedded battery still limits my options and forces me to have to plug the phone into a charging source. Whereas with a user-replaceable battery I maintain the option to swap it out on the fly to get back to a full charge within minutes (something not even fast charging is able to do). Personally I find that option invaluable as it not only keeps my phone untethered at all times, but allows me the freedom to use it as hard as I like knowing that spare will be back to a full charge faster than I can drain the one in the phone. Rinse and repeat that cycle as much as wanted/needed.
Also unlike a sealed/embedded battery, no worries about managing the charge level hoping to maintain its longevity, or having to deal with one that may be losing its capacity, or worse one that just goes bad. Instead I can have multiple batteries (as many as I want) to spread out the wear and tear or just use and abuse them without worry as they can be easily replaced (at minimal cost).
As to the Note 5 design, I really hope they DON'T go with glass-aluminum. Instead maintain a similar design language of the Note 4 with the metal sides, anodized but no paint and make the back softer and more rubbery for a better grip (no case, I prefer to use it naked).