The biggest threat to the Amish in Lancaster, PA is simply the cost of farmland. There is less due to development Amish families are larger than average American families. This has caused farmland to spike in cost and pushed Amish in to the trades. The exodus of Amish to form new communities in other states has been going on for 30 or more years.
Upstate SC has a growing Amish population due to the larger farms to be bought at a reasonable price. This has been a trend over the past ten years....Horse Farms especially. Right across the border in Tryon, NC is horse country.