Arcane Hierophant Variant: Archivist prestige class creation

I’m planning on creating a prestige class based on the Arcane Hierophant. The Arcane Hierophant however is more wizard/druid bias and since I’m an Archivist I decided to create a variant with the Archivist in mind.

The problem: I can make the prestige class continue the advance of the Archivist’s Dark Knowledge but I’m torn if I should add more class abilities. Is the continued advance of the Dark Knowledge enough? Or should I add more?

The BAB progression will follow the usual Mystic Theurge, same with the reflex, fortitude and will saves. The entry requirements would be two Knowledge skills (arcana and religion), ability to cast 2nd lvl spells (just like AH), and have Dark Knowledge as a class feature. it will have a d4 as its hit point gain, 4 + Int for its skill point gain. No alignment requirement and a +4 BAB to qualify. I’m still playing around some hypothetical abilities like the loremaster’s secrets class feature.

It’s the divine half I want to substitute with the archivist, so the druid part would be replaced by archivist.