I'd say it's pretty safe to bet that the next console will support external harddrives again, they have they tech for it.
I just think having an extra hdd internally would be benificial, if you want to take your NX with to a friends house you won't forget it, and if you don't like having to see the external hdd it's hidden. But they'd have to have the space inside the console for it, so the extra internal hdd is rather unlikely (sadly).

I don't like the concept for the PS4 that much, because you can't just add space without losing 500GB (or 1TB depending on your model), eventhough I like that you don't see a hdd hanging out beside the console.

*Popularized mainstream touch screen use*

*popularized motion gaming*

*used extremely proficient 100% lag-free companion streaming tech with the gamepad*

*ushered in glasses-free 3D*

*lags behind in tech anyway*

Yeah let's pretend Nintendo hasn't achieved anything technically in the past 10 years because you personally didn't like it. They are definitely going to do an all digital console. And it's going to me a massive, industry shaking success.

They've never had to. Now they have to.

I wouldn't necessarily agree to that. They value storage capacity, just not as highly as other things.

N64 they valued higher piracy protection + control over the media + loading times (cartridges) over storage space (CD)
GCN they valued higher piracy protection (proprietrary mini DVD)  over storage space + paying licensing fees (DVD)
Wii they valued higher piracy protection (proprietrary DVD) over storage space + paying Sony licensing fees (BluRay)
Wii U they valued higher piracy protection (proprietrary BluRay) over storage space + paying Sony licensing fees (BluRay)

So Nintendo so far tries to limit the costs for making games, by generating more sales through less piracy or saving the money for licensing fees.

HDDs weren't much of an issue previous to the Wii U for Nintendo.

Specifically concerning the Wii U:
Nintendo said that one of the design philosophies for the Wii U was to make a system that consumed little energy, so that mothers could be happier. 
Putting that into perspective, it made sense to use flash storage over a physical hdd. Flash storage consumes less watts, is smaller and produces less heat. Yet due to how expensive flash storage was/is I guess they could only afford a small drive (8GB and 32GB). 

After the Wii U Nintendo should have learned some lessons concerning the internal storage.
-consumers complained about the limited storage
-consumers bought the version with more storage
-3rd parties should have told them that they need more space by now

If Nintendo uses a SSD the space will be limited again, but they should be able to afford 128GB or 256 GB. I also highly doubt they will continue the two model strategy, because the basic pack Wii U didn't sell. But since 500 GB and 1TB HDDs are so cheap in comparison they should prefer those, except if they need the benefits of an SSD for the OS/console design.

The 8 GB and 32 GB eMMC NAND chips used in the Wii U were upper-mid range in Samsung's capacity line up at the time Wii U was being designed.   8 GB is now their smallest capacity eMMC with 256 GB being the high end.   So for the same costs, they could use 64 GB to 128 GB.

Also, if they switch to Samsung's new V-NAND (which I suspect they are), capacity starts at 128 GB which is also preferable because the read speads go from 300 MB/s to 1500 MB/s (BGA format).  They are slightly bigger but use almost half as much energy (something Nintendo seems concerned with).  Price doesn't seem much different as SSD's using both technologies cost about the same.

Why?

Well, the size of the games keep geting bigger. it's been impressive they have managed to keep most of their games under 5Gb this gen, but if the bigger games plus the DLC and updates, there is a really big need for space.

Why?

Consider that Nintendo had the first console that had day and date parity with all retail and digital games with the Wii U says otherwise.   Sony and MS didn't go day and date parity until after Nintendo bespite their consoles having massive hard drives.

However, I do agree that Nintendo puts far more emphasis on energy efficiency than MS or Sony but it's not related to their policy on digital distribution.

Digital only.