Cat III autolands will probably happen when the Galleleo satellite system comes in to operation. I understand it has a guarantee of reliability and accuracy compared to the GPS system which doesn't.
This will then reduce the RNP down to the required level for autolands.
The current cost for an ILS installation is over $1 million. Cost for a GBAS system which allows for unlimited "ILS" approaches in a 23nm radius is also #1 million!
Oz