According to Blizzard, they clarified that gamers who wish to take part in Diablo 3’s Seasons mode will not need an active subscription to the Switch Online service. “I see there’s some confusion about the necessity of the Nintendo Switch Online service in relations to the upcoming Diablo III: Eternal Collection. To clarify, access to playing Seasons does not require a Nintendo Switch Online subscription. However, access to online multiplayer does.”
They also note that this is essentially the same as the Seasons mode on the Xbox One and PS4. “This is identical to the way gameplay features function for the Xbox One and PS4 versions of Diablo III as well. Hope this makes the situation more clear!” This is good news for gamers who don’t wish to pay for the Switch’s online subscription service, but yet doesn’t want to be locked out completely from all of Diablo 3’s features. Diablo 3 for the Nintendo Switch has been confirmed for a release on the 2nd of November, 2018.