In fact, Blizzard is bringing all of Diablo III to the Switch -- the entire Eternal Collection. That consists the base 2012 game itself as well as both expansion packs, Reaper of Souls and Rise of the Necromancer. Blizzard is even throwing some Zelda-themed items as Switch exclusives.
As with the existing console and PC versions, players will be able to take on the dungeons of Sanctuary with up to three friends. With the Switch's modularity and mobility, there are a number of ways this can take place. The development team has managed to pack an entire controller's functionality into each individual JoyCon. As such, you can get all four people playing on a single Switch, wirelessly link up four individual Switches, or play remotely over the incoming Nintendo Switch Online service. If you want to get really fancy you can have two people playing on a television using a pair of Pro Controllers and another two using a separate Switch in kickstand mode, each playing on a single JoyCon. You'll get all four people in the same room and same instance, just not on the same screen.
Best of all, Blizzard isn't implementing its DRM, which demands an always-on internet connection, for Diablo III on the Switch. That means you'll be able to play anywhere you want, whether or not you have connectivity, and simply update your progression to the Switch's cloud once you're near a hotspot again.
Now, the bad news: There won't be cross-platform compatibility available at launch so you're all going to have to be on a Switch (or Switches) to play together. There's also no ability to import your existing DIII characters, but the team hasn't ruled out incorporating that feature into future updates.
I was recently afforded a quick demo of the Switch-based action and the Blizzard team appears to have faithfully translated the game onto its new platform.
Overall, I came away from the demo impressed. The gameplay was just as I remembered it from the PC version, the game looks and plays nearly flawlessly. Granted, the onboard graphics capabilities of the Switch are nowhere near what the consoles or a gaming PC can offer, but the onscreen action does not noticeably suffer from the GPU downgrade. The level 45 Demon Hunter I was playing with just mopped the floor with her undead foes. There was no noticeable jittering, video stutter or slowdown. Plus, the skill bar from the PC and console versions can easily be mapped to the XYAB keys so you can quickly tailor your skill loadouts as the situation changes.
My biggest qualm has to do with how reflective the Switch screen is. When playing through the first Act of the game, which is already pretty dark to begin with (being set in an underground crypt and all), I found myself squinting at the screen, trying to peer through the glare. When I did manage to spy the onscreen action, it was overwhelming. This is thanks, in part, to my teammate constantly spamming a meteor-based AOE attack which more than once caused us to become separated. We'd then spend the next few minutes backtracking our steps, looking for one another -- another favorite DIII activity. As such, even with the Switch's mobility, I'd recommend playing either on a proper television or at least out of direct sunlight.