Lots of things actually

- ogcd Shield Bash (though rather than stun maybe something interesting to the rotation)
- Salted Earth in its entirety, endlessly more creative than what we have now
- HP spender Dark Knight as a concept as a whole, make it the real lifesteal tank
- Seraph Strike, for all the reasons you already mentioned
- DOT spreading on SCH. We had Bane, why is it gone. Make SCH great again.
- Like Fawkes says, cards yeah. Though if we have damage-enhancing cards, make them part of a separate draw from the defensive utility ones.
- Kardia doing diff effects based on your action (Dot generating the shield is amazing)
- Marksman's Spite, purely because I love Sniper Rifles.
- BISHOP. AUTO. TURRET. As MCH's party utility for damage increase. Enough of this selfish MCH, just bite the bullet and bring this in.
- Black/White shift gameplay as a fundament for a more creative RDM. Not as damage vs survival but rather managing black and white mana in a more creative way (like intentionally overshooting on Black Mana for an ability that spends only black mana and lets you build more white mana after using it).