It will be really great if F/J and some top elites will get to use the China Airlines lounge, which is really nice. However, from the language of the e-newsletter, the lounge access will possibly be limited to possibly F/J passengers and top elites. I presume some elites in economy may just get restaurant vouchers. I can't imagine China Airlines lounge being able to handle all these additional passengers.
In terms of other Oneworld lounges...
The only one I can think about is the Sakura lounge operated by Japan Airlines. However, the lounge is relatively small and is located in terminal two.
The other Oneworld carrier that operates into TPE is Malaysia Airlines, which actually uses China Airlines lounge in terminal one.
I guess I am in the minority and actually like the more private first class lounge, even though it is a small room. However I am fine with a nicer lounge, if they are as great as the new Bangkok and Haneda lounges.
Carfield