It depends.
I mean, Flash is still *very* expensive per gigabyte compared to mechanical.
And for that to come down flash needs to be built on a lower fabrication process, however the side-effect of that however is you get reduced drive longevity due to various factors such as electromigration and general leakage.

As for digital, well, the market for physical is indeed decreasing in the face of digital, however there is always a large group of people who are adverse to change and people will still probably wish to continue to use last-century optical discs for their movie and music needs anyway.

The other issue with carts was cost.
An optical disc costs mere cents to produce, where-as for the kinds of data we will require for the next generation will probably range in the hundreds of gigabytes, flash will thus cost in the realm of $20 or more.
Thus, the cost will probably be passed onto the consumer if that is indeed the route that they take, online pricing will then match those prices to keep brick-and-motar stores happy.

Saw the thread. Have to say. Next gen will be PS service and XBL service. Server run. No hardware. It will start to happen in last 3 years of this gen. WAY cheaper.

*Raises his hand*

I don't trust digital only ownership. And never will. I always think that something can happen and that I'll lose it all. With physical I don't have that worry.

Of course on PC not going digital is not an option, but I keep my fears reassured because I only buy the games when they are dirt cheap (Steam Sales and the like).

Well, we are talking about 2020 here... We can't really forecast how the world will be in 6 years, this is close to impossible these days, sadly.  As more and more devices use flash, it will automatically go down in price and that really is a good thing. I don't want any mechanical stuff in my computing devices.

So I am mixing hope with quite an educated guess

There was also a large group several years ago which didn't want to have their email at the provider but get it theirself via pop3. Nowadays most people use imap. 6 years ago cloud-storage was close to unknown, nowadays many people use google drive or dropbox. People get used to stuff quite fast, it seems.

32GB RAM, 12 to 16 CPUs, 4k becomes standard.
Flash drives will become much cheaper and available as standard storage device for games, music, movies, etc.
Games all via download, PS and XB online services grow exponentially. 
The end of physical games will save on storage and production costs of games and hopefully the savings will be passed onto consumers with cheaper game prices.

This won't happen, believe me

Solor energy everywhere. Hybrid vehicles for everyone. Green Energy. USA! USA! Didn't we hear this shit like 10+ years ago. Hmm still fracking and Oil is king. Yep. 2 different industries yes, but all run off of this thing we love to call CAPITALISM+TERROR+FEAR. I'd rather install my 50+GB PS5 games off of disc by then, than take a chance on progressive ideas run by wall street jokesters.

VR will be dead by then.

The PS5 will not be able to play most games at native 4K. I predict 2560 × 1440 will be the norm maybe somewhat higher. PS5 will release in 2019 for 400$

12 GB GDDR5 ram and 4 GB DDR4
AMD APU again

Probably digital only

Power, as in Watts is going to be an issue. Silicon semiconductors are hitting a power wall. I expect a future console would be limited to similar wattage as current gen (~150W max, ~80W idling). Could be even lower due to energy policies in some countries. That will actually be the constraint on how powerful a console in a box can be.

So within this time frame we might have dark silicon (transistors on a chip that can't all be turned on). That means you can build in redundant technologies that you turn on when you need them. If you need more CPU power you turn on some CPU cores, if you need more GPU then you turn off a few CPU cores and power up more GPU cores.

Performance scaling I think may come from more specialized cores. Think the way a GPU is order of mangitude more efficient than software rendering on a general purpose CPU. If we will have ray tracing, then I expect ray tracing cores (RPU?).

You can see the difference in efficiency of CPU vs GPU vs ASIC in digital coin mining, ASIC can be 10X or more power efficient than GPU, and GPU can be 10X or more power efficient than CPU for the same work (* with exception of coins designed to beat this pattern *).

So I expect we will see less silicon devoted to CPU, more to GPU and to special purpose cores & decoders on chip.

There is no need for GDDR5 when DDR4 is available :)