During their first Campfire Chat livestream, Blizzard has announced that they will change Gems into crafting material in Diablo 4 in the future to combat stash space issues.
Campfire Chat Summary Missing Diablo 4 Gem Bag Ignites Community Discussion
Gem storage has been a hot topic since the release of Diablo 4, with many players asking Blizzard to add a Gem tab to the inventory.