When TH came out, I was expecting Spirits and Mii Costumes at best, since it wasn't confirmed at the time that DLC would go beyond the Fighter's Pass. However, what we got instead was a Spirit event for Mother's 30th anniversary; no TH-related content anywhere.
This leads me to believe that a TH character is going to be part of the post-pass DLC. Who do you think is more likely? Byleth, Edelgard or neither?
Personally, I'm placing my bets on Byleth, since he's not only the most unique avatar in the series, but also a general candidate for a unique FE rep, what with Brawling, Faith magic, the Crest of Flames, Battalions, and the Sword of the goddamn CREATOR!