fantasy:
Standard app that can be used to collaborate via whiteboard, buzz (for intercom) and audio/text chat in real-time between Swtich units (easily triggered while the switch is in 'sleep'), working over wired or wireless LAN locally in the home. With the ability save the collabation or chat in standard formats on MicroSD. Who cares about internet: it would be a half-hearted affair if it comes from Nintendo and their license agreement will mean you'll have to sell your soul to send messages over internet anyway (much like all the other spyware apps on Android or iPad/iPhone). LOCAL is fine. No personal data sent over someone else's server. So essentially a far more advanced real-time Pictochat.
reality:
Nintendo will end up disappointing us all on the apps front. Like always. We have so many devices that do what we want that will probably be a lot lighter and smaller and thinner and often have better hardware and countless apps. We can save website videos and play every video & audio format known to man, plus have a great choice of browsers, too many apps, etc. I really don't care if Nintendo has none of this. We have it already & the Switch looks too big and fat and limited to carry around instead of those devices.
Anything Nintendo offers would pale in comparison. The advantage they have with the Switch (to make people buy one for themselves after seeing their friend's) is to leverage multiplayer/multi-user collaboration as much as possible & make it standard, in both games and apps. Any apps that are fun and useful between 2+ users would be great. But I suspect Nintendo will not want to pay or spend too much development time to build in anything too elaborate or useful.