Delta has been running an announced sale to and from TPE, but as discussed in other threads, there is speculation that the route isn't doing well given competition.

It is unfortunate that DL isn't selling fares through TPE connecting elsewhere in Asia, and sticking to ICN. We are doing separate tickets to connect to Vietnam-- even though two Sky team partners serve Vietnam from TPE, DL won't sell it as a revenue or miles flight.

Four Airlines to operate Taipei-Seattle