Tons of concerns and curiosities obviously, but personally with how well this looks, I'm hoping they have all the right answers for online, storage, and the other minor things.
I've heard some rumors about Nintendo working very hard on their online services, I watch the job market for these types of things and Nintendo has been on quite a hiring spree lately for these types of positions.
Storage I'm very very curious about. For home console gaming, I see no issue with using external hard drives, that is what I do in most cases (curse you PS4), but being able to have that digital content/patches/install files on the portable device, it is definitely a concern. Nintendo does have a history of making their games play straight out of the box, so hopefully that will continue. Flash media is going places, you can get 200GB flash cards for about $60, games don't usually take more than 40GB. You can get a 64GB flash card for about $20, and that's consumer prices. I don't believe it costs more than a few dollars for these companies to produce these cards, so it wouldn't be unreasonable for Nintendo to design a flash memory based board capable of storing upwards of 128GB while still maintaining an effective cost to price ratio. With the 3DS for instance, I don't think it was ever a size limitation issue so much as what the system itself could handle. And looking back at older cartridge systems, they were much more expensive to produce compared to today