In Rarran's video today with Celestalon, specifically the section about the revealed cards Celestalon mentioned some things about the development of some of the recently revealed cards here are some that I found interesting

Sunfury Stalwart was originally a 6/8 but didn't have rush (presumably changed as a buff)

Invincible was originally (or at some point) 7 mana (Nerfed)

There is some specific ordering in place for dual tribal tags (all that was specifically mentioned is that undead goes first)

Scourge Rager was originally a 5/5 but apparently was "too OP" (I guess there's a rallyesque card this expansion that it's really good with)

He pretty much confirmed fire warrior (when talking about embers of strength)

Not particularly notable but apparently corpse explosion's rarity was changed last minute (was an epic I'd guess)

Vampiric blood was considered to be nerfed to 3 mana late in balancing but wasn't

Just found this interesting