I tried to make peasants pay taxes. And found that it is not possible. Here is the peasant “mod”:
"core:peasant" :
{
"cost" : { "gold" : 4 },
"abilities" :
{
"tax" :
{
"type" : "GENERATE_RESOURCE",
"subtype" : "resource.gold",
"val" : 1,
"propagator" : "PLAYER_PROPAGATOR"
},
}
},
But those peasants refuse to pay tax 
I tied it with various propagators and without propagator. No tax. But i think it would be just consistent to have creature abilities of such types.
For propagators, useful ones here would be PLAYER_PROPAGATOR (should be the default one if not specified), TOWN (then only generates gold if in town) or HERO (then only generates gold if in heros army). Also it would be useful to have limiters applicable here too. These limiters then need to be attributes of the propagator target. So f.ex. if the propagator is HERO, then limiters might be a secondary skill, a specific here or a faction or hero class. If town is the target, then having built a specific building would be necessary. Here f.ex. having built the market place. Or faction may be useful limiter. Or alignment. For player propagator, a specific player may be a useful limiter.
These ability settings would be useful for another project too. I’d like to add a creature growth bonus to heros with creature specialty. But obviously for their specialty creature only. So here again i need a bonus limiter. For creature growth the correct propagator is VISITED_TOWN_AND_VISITOR. What i need are limiters. A specific building built is a natural limiter. But a faction limiter is necessary too.
So do those limiters already apply to the propagator target? Or would that need a limiters subsection in the propagator struct? Would at least be consistent this way.
Very similar would be artifact bonuses with similar limiters. The default and natural artifact propagator is the hero. So what about skill levels limiter? What about specialty limiter? What about creature type limiter, giving such a non-battlefield bonus only if hero has such creatures in his army? What about artifact limiter, giving bonus only if hero has this artifact equipped? In case of town propagator, same limiters as above. Some bonuses here (resource generation) would be much easier und much universal, the faction main resource could be a limiter too.