The main concern from US is passport security. Before TW changed the application procedure, one who applies for new passport is not required to present personally at the office. Not the case anymore. They also put an ID chip in the passport cover, just like the US passports, to make it more secured. This was the major road block in this matter. Now that it is resolved, it's very likely that ROC will be one of the Visa Waiver Program (VWP) countries latter this year.