I feel like adding fire to warpriest is an interesting idea (especially as it also makes it more different from warsoul), but for it to work out, we need either fire based SLAs (as taking metamagics to actually be a fire caster while having no SLAs for leveling does feel bad), or buffs that emulate metamagics while using melee/ranged abilities from the tree.
For example, if you hit with radiant florish, your next (fire?) spell counts as being empowered (not stacking with actual feat). Or an enhancement, that grants a metamagic feat while having a weapon feat (like Improved Critical for empower and a greater fighting style/IPS for quicken), so that this combination of melee and ranged would work out better.
Which would mean to also take warpriest under bigger reconsideration, but we're at cleric atm anyway. :P