DefenseNews has an Intercepts Blog up asking why Taiwan is publicly seeking the F-35 when it is already unable to get the United States to sell F-16C/Ds to the island nation. I'd say Taiwan is practicing Rule No. 1 of bargaining; ask for the sky, and wait for the counteroffer which is closer to what you actually wanted in the first place.
Just one more thing to add: Taiwan needs to sort out its defence policy, and the politics behind it though. That could very well prove tougher than persuading the United States to sell defence articles.