If Nintendo release anything LESS than 500gb, then it's a mistake.
I think minimum 1TB is necessary for gaming now.

What would be cool to get:
Compromise between affordable SSD storage (250GB might be too expensive) with expandable SDUHS/USB 3.1 typeC option.

What we will get:
Continue with the 32GB but give expandable SD/USB3 option.

Not if updates and save files are stored in the game card.

It's bound to get even better on the NXDS, too.

The game size for Wii U games are quite small, but compare it to the game sizes on the PS4 and XBone. They are somewhere between 30GB and 50GB and can be even larger, on the Wii U the games are far smaller because the texture file sizes are smaller. 3rd parties will also want to have a full install on the hdd like on the PS4 to reduce loading times.

I think the NX should aim for 1TB+, and have easy ways to upgrade the space.
I'd love it if you could build in an extra hdd and add usb 3.0 hdds additionally to the one built inside. (Not replace it like how the PS4 handles it)

Nintendo has never really valued storage capacity. They'll probably have two models: a basic model with 16GB and a premium model with 64GB. It will be compatible with HDD's of course for more storage.

Bare minimum sounds exactly like Nintendo's hardware philosophy. The Wii U had an 8GB model. Nintendo will never overdo something when it comes to hardware specifications. I guess I can see them do a 32GB basic model, but can't imagine them going any higher.

I think 1TB is a pretty safe bet, and I think it'll be easily upgradable. Just don't know if it will be internal or external again like with the Wii U.

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.

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.