I've been thinking this over, and having yet to see the new CoM, i could be completely out of my depth here.
So disclaimer out of the way here's the idea; (if it's not too late already)
Clerics. Most importantly their religions
(TL;DR version at end)
I find the cleric class somewhat lacking in HARP. to me they seem like just a mage with a different school of spells they can learn and a slightly different skill subset.
I would like to see a system put in place for religious belief. (doesn't matter what campaign setting you run)
my basic idea revolves around the concept of a FAITH stat.
how you work this out is subject to debate but it should be in the realm of 1-100 with starting characters about 5-10
then as a cleric. all spells you cast have their effects increased by the recipients FAITH stat. (in various forms)
I.e. healing spell heals Xd10 hit points + recipients FAITH
Strength buff has it's duration increased by 1 rnd / 10 points of recipients faith etc.
bless would give a bonus of +5 (+ recipients FAITH stat)
obviously all these bonuses need to balanced and play tested but the idea remains the same.
obviously this only works if the Caster and recipient are of the SAME organized (or disorganized) religion.
Another system that can be implemented is that people of opposing faiths or enemy creatures such as demons/undead etc
have their resistances reduced by set amounts in a similar fashion.
casting Turn undead would give a bonus of 2 turning points / 10 FAITH of the caster.
religious conversions can work in this way too. say a non believer is dramatically cured of a horrid disease by a cleric of religion X,
Then he makes an RR against magic - the Casters FAITH, if he fails he gains FAITH points in the CASTER's religion. (the exact quantity can be determined by various means like how much he failed his RR, the severity of the effect etc. )
If a person gains more FAITH points in the new religion than he has in his old one, he converts.
Basically the idea is to give specialist clerics an edge over others who learn the spells by other means and giving them a system to actively pursue their religion's beliefs/agenda's and spread their teachings.
TL;DR VERSION;
implement a FAITH stat. use this stat to give Cleric's minor bonuses to spells from the Cleric Sphere only and to aid in religious conversions and the like.