DnD Beyond has a different licensing deal than Roll20 (or FG for that matter). The seem to be tied far more closely to WotC, sharing resources and marketing. I mean, their name alone pretty much indicates that they are associated with the D&D brand, which likely has the benefit of giving them better access, while the drawback of "sink or float along with WotC". That being said, Roll20 is dedicated to converting as much WotC content as they can, but is loath (or contractually forbidden) to comment on deadlines and projects in production too far ahead of publish date. TL;DR: You're not likely to get an answer unless the date is very close. :)
