I'm not optimistic at the staying-power of this initiative. There've been a few things like it before, like a journal dedicated to asking authors to submit more informal "ELI5" versions of their popular papers for broader appeal. But the incentive structures in academia continue to favor only "original research". Just like expository papers aren't valued by hiring committees, grant reviewers, etc, submissions to this journal won't be valued.
Terry Tao is on the board of scientific advisors and posted about this a couple days ago: