Don't have the DMG handy but somewhere in the back it talks about this exact thing.  It basically says it's okay to trade armor proficiency for Unarmored Defense from monks.
		
		
	 
Hmm... still not exactly thematic to the particular domains, but if a cleric absolutely *must* have some sort of defensive ability in that slot, I like it better than heavy armor proficiency.
	
		
	
	
		
		
			If I were to get rid of heavy armour for life, nature, and tempest clerics I would also change divine strike to potent cantrips and make the change from a cleric that is competent in melee to a cleric that is competent with ranged spell attacks.
		
		
	 
I'm not sure that's really necessary since divine strike can be used on 
any weapon attack (not just melee). Also, the parallelism of the different domains giving different types of bonus damage is an aspect of their design that I liked.
	
	
		
		
			The life domain cleric would gain spare the dying as a bonus cantrip and the tempest cleric would gain thunderbolt as a bonus cantrip (firebolt but lightning damage).
		
		
	 
Spare the dying as a bonus cantrip could work. It's touch-range, though, so it would still require the cleric to get right in the mix instead of providing support from the sidelines. That's why I suggested letting them 
cure wounds at range.  I'd still like to know what people think of that idea. (If it's too powerful, maybe a compromise solution could work -- give them 
spare the dying as a bonus cantrip, but with a 30-foot range.)
Thunderbolt is a nice concept, but the name implies thunder damage. (Plus it sounds too similar to their 6th-level Thunderbolt Strike ability -- which also does lightning damage. Go figure.) You can't call it 
lightning bolt for obvious reasons. How about calling it 
shocking bolt and giving it the effect of 
shocking grasp with the range of 
firebolt?
The only idea I've come up for Nature clerics is to give them either 
animal friendship or 
speak with animals at will (or maybe once per short rest) and sub in 
entangle as a bonus domain spell. That might step on the druid's toes too much, though, and I'd rather give them something that's unique to them.
Thoughts?
Wyvern