So....
https://fireemblem.gamepress.gg/datamine/feh-datamine-110
-Micaiah apparently has Distant Defense, Guard and Drive ATK.
-Sothe is practically Jaffer 2.0. Even with the same skills like Glimmer, Life & Death and Spur ATK/SPD.
-Zelgius is Black Knight 2.0. He has everything unique from Black Knight, but he has Fierce Stance and Panic Ploy instead of Steady Stance and Wings of Mercy. In comparison to Black Knight in terms of Neutral Stats, Zelgius has -2 HP, +2 ATK, -1 SPD, +3 DEF and +3 RES.
-Oliver has a Blazing Skill, much like most GHB enemies. His skill is Blazing Light. He also has Mirror Strike(+4 ATK/RES when attacking) and ATK Ploy. He can give Mirror Strike 2 at 4*.
Also, there appear to be new Arena maps, either they are available now or they are coming out later. One of the biggest notes is that there is going to be a new space that actually stops horses apparently.
Basically, Horse Emblem is going to be messed with hard in later maps, as those things can also appear on Defense tiles, completely preventing cavalry from using them.
Also, another thing to note is that in the datamine, there is a Daily Login "Comeback Talk" conversation involving a character named Sharon.
I haven't found any images of this Sharon character. Also, I did check the wiki and there doesn't seem to be any info of a Sharon other than a character from a TearRing Saga game. I also checked the Cipher card game as I remembered that there were OC characters who apparently came from Askr, but none of them were named Sharon either.
Edit: Actually, I realised that it could just be Sharena and not a new character.