Developers will still be the same next gen. I wouldn't call them lazy, but pre occupied with effects, screenshots and multiplatform engines. And sure the early games this gen should run fine in 4K, but will the optimized games at the end of this gen + another lick of new paint still manage that. Real time ray tracing is still a goal to be achieved, that definitely won't be running in 4K on next consoles.
-The thing is 4K isn't as big of a deal as one would initially think. If a gpu's architecture is optimized correctly for a given resolution it can make a big difference. For instance the 290X is only ~30% stronger than the 7970 in 1080p, but in 4K it becomes 50%+ at times and even matches the 980. The 390X is going to use HBM memory on a 4096-bit bus and it is only the first gen of HBM. Plus AA really won't be needed anymore so that will help quite a bit.
-I did say 16-32GB of RAM so I think it could be somewhere in-between. I believe 16GB would be enough to skimp by a little better than the PS3 did, and 32GB is far more than enough just like the PS4.
-Remember SSD's are expensive now, but their prices are changing rapidly. 2 years ago a 1TB SSD was $4000, a year ago it was $1000, and now it is under $500. They really might be at current HDD prices by 2019.
-They went with an 8-core at 1.6GHz because they had no other choice. AMD is the only vendor who can provide both a decent GPU and CPU in one package. The bulldozer family was a complete failure to the point that clock-for-clock the Jaguar cores in the PS4 are just as fast as the big desktop processors AMD is currently trying to get rid of. Then consider that 2xjaguar clusters only use 40-50w and the 1.6GHz models are dirt cheap and have a respectable amount of horsepower behind them. If used correctly a 1.6GHz 8-core is just as fast as a 3.2GHz quad-core, and better at lower framerates with lots of data onscreen. What gaming devices tend to push as much crap as possible at the expense of a lower framerate? -> Consoles.
Now you could make my same argument for why they would go with 16 cores instead of 8 faster ones, but things change a little. Utilizing 6-cores in a game as been done for a long time since the 360 and PS3 used 6-cores for gaming anyways (2-cores in the PS4 are used for background tasks). However 16 has never been utilized that well in gaming so far. Also by the time the PS5 comes out AMD's low-power cpu's should be ~3-4GHz (The newer ones are already at 2.4). I am just assuming Sony will continue to use the same types of products, and in 5 years I don't think many things will even be buyable below 3GHz lol.