Could Guam, one of the 5 U.S. territories, become a state? Absolutely!
That decision is up to the people of Guam. There are about 175,000 people living on Guam.
People born on Guam are American citizens as Guam is a part of the United States. Guam is not a different country, nor is it "owed" or "governed" by the U.S. federal governement. Guam is run and governed by its own elected government, which includes a governor and a legislature. The postal code for Guam is "GU," just as the post code for Califorina is "CA."
Every so and so years the residents of Guam vote in a referendum about their jurisdiction's political status.
Currently the majority of the population favors the status quo (ie. remaining a territory).
There are in fact cons to becoming a state. One such con is having to pay federal income taxes.
Some Guam people who oppose statehood argue that Hawaii has lost out by becoming a state. They see Hawaii as having lost its local culture and identity by becoming a state.
The U.S. territories of Hawaii and Alaska become states as recently as 1959. So when Pearl Harbor was bombed it was not the state of Hawaii that was attacked but the territory of Hawaii that was attacked.
Just about all U.S. states were U.S. territories before the residents who lived in those territories voted in favor of coming a state, and then after successful negotiations between those territories and the U.S. federal government, became states.
Guam is a major tourism hub for East Asians who go there to enjoy Guam's tropical weather and beautiful beaches.
Ask anyone who has been to Guam and they will tell you that Guam is a state in everything but name.