@Gandalf
Yeah, a list a long these lines is great. If you have something around that shows how they look in the debug log that would be perfect.
Well, as for ideas I have so many myself, otherwise I would't have made it.

But I certainly don't object to some brainstorming
Make some units like angels or devils more expensive or cheaper as you dominion grows (scores)
Give a weak nation a gem discount site that looses the discount when it's taken by another nation (debug log)
Changing mages based on your conquest (you have taken Mictlan cap and all your nationals have learned a bit about blood) (debug log)
Gem gens - make them spells that can be cast at provinces containing specially prepared sites and increase the gem income from the site. Make them more expensive with every turn/casting (debug log)
@Stavis_L
Atm I don't provide any way to access messaging options. Well, to be honest, atm I don't really provide access to anything, except through copying the examples.

Theoretically such a thing could be coded from scratch by anyone, and maybe it will be added in a long time, but I'm not sure if it's worth it, since it would require changing 2h files.
A immortal messageboard (who needs a starting scout anyway) is imo the best thing as you can use it to deliver both messages and gems (in an ugly way also items, if you give them access to exactly the paths needed for forging that for 1 turn, just look at the researchers mod) without messing with the turn files themselves.
The conditions in the scorefile are
Forts
Provinces (change
Forts | to
Provinces | )
Income
Gem Income
Research
Dominion
Army Size
Victory Points