I was playing around with battlemages in a seal of the righteous style build. Seal benefits from SP more then AP by default and can trigger on smite with a judgement talent. It was very weak on AoE.
If I remember correctly: When you cast a spell your auto attack begins its internal cooldown until next hit after the spell ends. Instead with battlemage, if the internal aa cd is done, the auto happens after spell cast ends.
So we would need to line up our auto attack swings to be slightly under our spamming spells. Or a rotation that benefits from cast bar into instant cast for the global window.
Possibly a poison and nature dmg, seals & holy, or firebrand and fire. Or any REs that combine them.
Does that help?