Update: It has been announced that The Isle of Armor will be released Wednesday, 17th June.
The Pokemon Company has announced via Twitter that they will be revealing further details about the upcoming Pokemon Sword & Shield Expansion Pass tomorrow. The company will be talking about The Isle of Armor and Crown Tundra at 10pm JST, which is 6am PT / 2pm BST. We shall of course be publishing the information once it is revealed. So far the first Expansion is due to be released some time at the end of June, but we should get a firm date tomorrow.