You can not use this house rule ... There is already a similar supernatural abilitie. Just use Shapechange to Zargon (Elder Evil pg 149) to access Divine Enervation.
Divine Enervation (Su) All divine spellcasters lose the ability
To regain spells as long as they remain within 100 miles
Thousands of Zargon. This interdiction does not interfere
With spellcasting.
Malefic Properties
Antimagic Field dont protect against it. The Enemie use Greater Spell Resistence (39 Natural SR +Caster Level)
You can create a combo with Divine Enervation + Violet Rain.