On its Facebook page, the Shadowverse team has announced its plans for a soft-launch:
The soft launch of #shadowverse is slated for release on iOS and Android in mid-June! There’s no need to sign up early; anyone who downloads the app will be eligible to play.
We plan to carry over most of your progress from the soft launch to the official release.
The soft-launch will allow Cygames to focus on final polish and bug fixes before marketing to the general public.