I mentioned this in my other post.
If alts are a reality and can't be removed from the game, my thought is that they are made an official feature in some manner.
Would making alts cost auth upkeep work to curb alting? Let's say, for example, that every character with a skill above 50 starts costing authority for the village they are oathed to. The upkeep scales according to his skill level, and also proportionally to the number of skills above 50. If it's not oathed to any village, the character has its skills capped at 50 until he's in a village again. And if village authority reaches 0, the idol is destroyed.
This should not be a problem for a regular village with a couple hq farmers, cook, crafter, and hunter, and much less for a hermitage with only two highly skilled chars. But botting would be harder, although not impossible.
The exact numbers have to be balanced. For example, with 50 ua you can't get the items you need for an idol unless you have help. And done wrongly it could make botting worse, for example by encouraging players to make hordes of foraging bots to supply the curios that will keep the authority up to support themselves. But I believe it's doable.