In a post on the game's reddit page, a Bethesda representative announced that the development on Legends has been put on hold for the forseeable future, but they plan to support the game with events:

We would like to provide an update on Legends in regard to new content. Our previous roadmap indicated we would be releasing one more set this year. We decided to put any new content development or releases on hold for the foreseeable future. This decision will not in any way affect the release and development of GAEA’s Asia-specific version of Legends, which is operated separately, but will inform our decisions on content and feature development going forward.

Until then, you can still download and play Legends on all existing platforms and compete online as well as in the single-player modes. We will also continue to support the game with monthly reward cards and regular in-game events. New expansions and other future content, however, are no longer under active development. We will continue to provide ongoing maintenance support.

To thank you all for supporting Legends these past few years, and for continuing to play with us, we are giving away The Tamriel Collection – an assortment of new, three-attribute cards and more – to all players for free upon their next login. We are immensely grateful to work on The Elder Scrolls: Legends, to have you as a community, and we sincerely appreciate the love and support you’ve given us.