Historically speaking, the admissions of states to the union generally came in pairs after the original thriteen British colonies.
1. The pairing of state hood admissions was done to balance power betweeen the southern and northern states, i.e., Maine, which was a part of Massechusetts until the Missouri Compromise.
2. During the American Civil War, West Virginia split from Virginia with Nevada quickly added to further isolate the Mormon dominated Utah territory. The Civil War allowed time for the Mormon population to become pretty strong economically and politically.
2. Hawai and Alaska, the 49th and 50th states, admitted to control the spread of communisim (both being admitted in the same year, 1959, the year the Cold War was reaching for its coldest). Alaska was a Russian colony until the gold rushes of the late 19th century made the population made mostly up of Americans.
The conditions for Puerto Rico and the District of Columbia to become states (current populist additions) do not have compelling conditions for their admissions. Puerto Rico has tried many times in the recent past and it haves failed.
No. I do not see added state hoods in my lifetime.