If you are planning to purchase Diablo III: Eternal Collection and do not have a Nintendo Switch Online subscription then you will still be able to access the game’s popular seasons mode. This will come as a relief to those who have yet to sign up to the service. The news was confirmed by Blizzard on the game’s official forum.
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.
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!