Diablo III: Eternal Collection for the Nintendo Switch will be released on November 2, 2018, which also happens to be the first day of BlizzCon 2018.
Announced via Twitter, Diablo III: Eternal Collection is available for pre-purchase on the eShop now and will cost $59.99 USD.
Source: IGN.com Diablo III: Eternal Collection Release Date Announced for Nintendo Switch