Borneo and Taiwan come to my mind. A long shot though.
I actually could see North Borneo (which would be modern Sabah) becoming something like Hawai'i and eventually gaining Statehood in the mid-20th century.
Taiwan would be out of the question; by the time we gained control of Taiwan is was the end of WWII and there was zero support for annexing territories like that, plus it would cause far to many problems diplomatically and there would be no support for it in Congress for several reasons, racism chief amongs them.
one that is actually plausible is after WWII the Island of oakinanowa (sp) It was in US hands for a pretty good while and had the pop. for statehood over 1million
Okinawa, and the rest of the Ryukyu islands for that matter (Okinawa is only one island among the overall group we controlled) would'nt want to become a State though, nor would it realistically be allowed, given English was only a second language of a small minority and legally speaking annexation would not go over well with the rest of the world and especially Japan (which by the 70's had become a close and important U.S. ally).
What might happen is Okinawa becoming an Asian version of Puerto Rico, that is being an Unincorporated Organized Territory with self-governance, but withe Statehood either controversial or not considered.