Damn, you win the prize for technology optimism. I mean, it could be done by including an second embedded battery that would hold a charge for 10 minutes
A suitable capacitor (perhaps a supercapacitor, for capacity vs bulk) might also be able to help briefly "bridge the gap" during battery swaps.
But even being able to run off a charger temporarily could help some users hot-swap batteries. I tried it with my G4, and it didn't work. The phone didn't instantly go dead when I pulled the battery, with using the LG charger, but it show a message, and then powered itself down.
Out of the other goals (48 hours of actual use, 7 days on a smartwatch), hot-swapping might actually be the most attainable, at least if using a charger was permitted for hot-swapping.
New battery technology always seems to be 1-2 years away, so I personally wouldn't hold my breath on that.
Better energy-efficiency could make better use of the battery capacity that we have, however, as evidenced by current phones with longer battery life. But that may be at-odds with having giant QHD screens, 6-8 core fast processors, etc. Though making the chips on a smaller manufacturing process could probably help us have our cake and eat it too.
If manufacturers focused less on phones being razor-thin, we could also fit larger batteries, of course. Maybe the industry will reach a tipping-point where people agree that battery life is too short, and will take steps to address it. They likely won't come "free", though, we'll probably have to compromise a bit.
There are waterproof phones with removable batteries & SD cards, like the Galaxy S5. So that could be achievable, if the manufacturer really wanted to go for it.