I hope there are plans to add additional classes and Races, specifically Satyrs and Bards. Such a fun combination I would LOVE running through a campaign with this.
Think they said they hoped to implement all the PHB stuff first. I'd guess if they go beyond that, next sources to look at would be Sword Coast Adventurer's Guide (because forgotten realms) and Xanathar's Guide to Everything. But so far they only said hopefully all PHB