Adding a dozen would take about 6 years.
At best . Because of all the work it takes they can do 2 new courses a year. If they doubled their staff they could do more. Plus they would have to find a dozen courses willing to be added to WGT.
We should be getting Pebble Beach for 18 hole stroke play in the near future. They did the photography needed for all 18 holes the first couple weeks in May last year.
We already have the 2016 UIS Open venue - Oakmont - so that frees up their time to do a non-USGA Open course for next year.