I note that by default it seems villages spawn growing two types of crops.
The first crop is always wheat.
The second is a root vegetable, either beetroots, carrots or potatoes.
Farmer villages are able to plant / re-plant crops, harvest them and pass excess plantable seeds or vegetables on to each other.
I have some questions about this:
I don't know if there are any differences between this version and console/java versions regarding villagers so my answers might not be 100% correct (I haven't done much with villagers in this new version).
1) Are the type of crops grown in a village a persistent attribute of that village? Otherwise it is just the type of crops the village spawned with and as a result the crops that ended up in the farmer villagers' inventories?
Whatever crops a village spawns with is all the crops that village will have without someone or something acting. So if a plant is harvested or destroyed it won't come back unless it is replanted.
2) Do farmer villages have and unlimited supply of seeds for certain crop types or can they run out of everything and be unable to plant / replant.
Villagers only have whatever seeds/plants that they have harvested. I don't believe they start with anything in their inventory.
3) Is it possible to successfully introduce new types of crops into a village and have the villagers keep harvesting and replanting it?
This should be possible.
4) Related to the previous question, do villagers have a limit on how many types of crops they can hold? Do they have any priority / preference of one crop type over another?
They have an inventory that has a limit to how many items it can hold. I'm not sure of the amount off hand. The wiki states that they will plant whatever is in the first slot of that inventory until empty moving to the next slot etc.
5) Can diverse ranges of crops be farmed sustainably by villagers? Will they keep planting all the types of crops they have? Otherwise, over time will they keep planting the crop they have most of until that crop dominates and becomes the only crop being farmed?
Looks like they will plant whatever is first in their inventory. For a variety of crops you would probably need a number of villagers each with an inventory full of that particular crop.
6) Is there any strategy for dealing with plantations in a village that end up getting ignored by villages (even though they spawned as part of the village).
I have managed to introduce new types of crops into a village by planting them in plantations that the villagers are ignoring.
I have had problems with planting new types of crops and the villagers harvest them but don't replant them again so I loose that type of crop from the village.
This probably relates to them planting from the first available slot.
The village I am currently in has degraded to the point the villagers are only planting carrots and nothing else. I am in the process of trying to establish new types of crops. Wheat had grown in the past.
Answers above in bold.