Do I want a monotheistic campaign setting? The short answer is, yes. The long answer is, be careful what one wishes for. If the defacto definition of ‘D&D monotheism’ would be the DM is ‘God’ and decides what the Infinite thinks, then that too would objectionable. God is infinite; the DM is less so. Basically, Divine Infinity exists beyond the fabric of space-time, simultaneously past, present, and future. In a monotheistic game setting, the Divine normally intervenes only subtly and indirectly, because, the Divine desires humans to make the world a better place by means of human effort. The risk to humans is real. The good that humans do is real. Normally God is hidden. God is most ‘visible’ when other humans are doing good things. In other words, if the DM wants to supply the team with help via some NPCs or items whose opportune timing is ‘miraculous’, that can be fine and fun. But in terms of actual game rules, monotheism is part of the background flavor without any need for mechanical rules.