Other implements use the weapon slot. Shields use the arm slot. The precident exists for class specific gear to use up an existing slot... I don't know that I like the idea of holy symbols skirting that precident and giving divine characters an "extra" slot.
I'm fine with standard symbols taking up either a neck or a weapon (offhand) slot, or with magic items for other slots that can be used as holy symbols.
I'm fine with standard symbols taking up either a neck or a weapon (offhand) slot, or with magic items for other slots that can be used as holy symbols.