SoM characters were 100% able to transfer on Classic Era realms. Get rid of class items/runes/any special SoD flavor themed thing, and revert the boosted tier pieces to their original values, I don’t see the big deal honestly, Era is 90% GDKPs and 75% slower combat. At least people get to keep the time investment they made.
Looking Forward
Finally, many Classic players have asked what will happen at the end of the Season of Mastery, and here’s the answer. When Season of Mastery concludes, you’ll have the option to permanently transfer your character to an existing Classic Era realm in your region. This free service will become available for a limited time at the conclusion of the season.
Blue post source;