I was doing my usual checks for new developer posts outside of the forums and discovered that Game Director Jeff Kaplan posted on Reddit to a thread indicating that the Arcade will soon be updated to have seven game modes available at any given time:
This is promising as it indicates that both Quick Play Classic and Mystery Heroes will remain as long-term entrees in the arcade while still allowing room for things like two seasonal event cards. Also as you can see from the spolier image, it looks like a new season of Competitive Elimination 3v3 will be coming (we have not had this Competitive Arcade mode since June of 2018).
That’s not all, in a separate post, Jeff Kaplan indicated they are looking to add achievement eligibility to Quick Play Classic as well!
This is very exciting news!