Project site part of a newly masterplanned area

I would say this is unlikely, as the intent of those high-priority options is to direct development to areas where development is typically more difficult (e.g. brownfield, economically disadvantaged area, historic area with preservation requirements). Developing in infill sites is addressed by Development Density. 

If the master planned area was designated by the local government as a priority zone for economic development, you might be able to document that as equivalent to the standards - more likely if the project is outside the US and you can demonstrate that the area is comparable to the priority designations referenced in the credit. 

The High-Priority credit can only be achieved by Option 1 Historic District, or Option 2 Priority Designation, or Option 3 Brownfield Remediation. Your project site is exactly cannot meet Option 1 Historic District either Option 3 Brownfield Remediation. The possible option is Option 2 Priority Designation. To achieve High-Priority credit through Option 2 Priority Designation, you must provide a narrative demonstrating how the priority area in which the project is located is equivalent in terms of goals and operation to the priority designations in the U.S., which are outlined in the LEED BD+C Rating System. For example, there should be a government runs program that must be provided to reward/encourage the development of certain appropriate projects on such sites to encourage investment in the area.