I was thinking more along the lines of 4 new hero cards that are the old gods:
Draw card and spreading madness for its mana cost. New damage-self cards printed to boost this effect.
Discovers a copy of minions to summon.
Crafts custom deathrattle minions.
After every card you play a random spell generates. Repeatable hero power lets you undo the spell cast for 1-2 mana.
Leaving the battlecries blank so i don't make an ass out of myself trying to balance everything. It would also be cool to see scaling hero powers that upgrade each time you use them. For N'Zoth an example would be *4* mana: ressurect *1* different deathrattle minions that died this game. Eventually it moves up to 10 mana full board of deathrattles, but importantly only one Kahtut Defender each batch.
Considering Legends of Runeterra made a strong impact im sure Blizzard will have to announce something for HS. Its gonna be a fun 2020. LoR success will also mean HS improvements which will benefit this game
We had the villain expansion and the hero expansion (from which the main villains were mostly absent), and the third expansion will be the final showdown between the two. The Old Gods factor in somehow. That's my prediction anyway.