IMO, WPL will not want to increase it's stake in Sunrise. I can think of many reasons
1. The opportunity cost of $350m - spend the money now and the asset does not produce a return for at least 10 years. Use the money now to progress Scarborough and Browse - get a return on the cash.
2. If WPL did pre empt, then the cost of development grows in relation to it's stake - so more capex would be required.
3. If WPL did pre empt, would Timor be so belligerent that attempting to progress Sunrise would just be very frustrating.
4. Would WPL be cast by Timor as the "corporate bully", not allowing the small undeveloped nation of Timor to develop it's resources and provide jobs and economic activity for the nation. You can just imagine the spin .....
HT1