If more than 25% of the population is opposed to it, it will never work.
If you admit a state with 40% irreconcilables, you are asking for trouble.
Do you really believe that everyone who votes against statehood is an "irreconcilable"? Are you aware that voting for statehood means voting for the imposition of federal income taxes? While I think that's a small price to pay for voting representation in Congress and the right to vote for President, many people vote with their pocketbooks. But those are the same people who might decide to move to the states to work for NASA.
When Nebraskans first voted on whether to become a state, in 1860, the question was defeated by 53.1%-46.9%. A few years later, the Republican-controlled territorial legislature petitioned for statehood anyhow, opposed by the Democrats, and Congress approved an Enabling Act setting forth the conditions for, and treatment of Nebraska under, statehood. The legislature submitted a constitution for the new state of Nebraska to the people for ratification, which was one of the conditions for statehood. The constitution was adopted by only 50.6% to 49.4%. Soon thereafter, Nebraska was admitted as a state. I do not believe that the large percentage of the Nebraska population that opposed statehood became "irreconcilables" after statehood was granted.
BTW, the Puerto Rico Independence Party received only 2.7% of the vote in 2004, which is about one quarter of the percentage of Alaska voters that voted for Ralph Nader in 2000. Puerto Ricans who favor independence will be no more problematic if Puerto Rico becomes a state than are Alaskans who favor Nader's socialist policies.
If even 10% are against it, it will never work. I say this as someone who was in the San Juan hotel when it was burned down by the Puerto Rican liberation group. More than one hundred people died in that fire. The head of the group that set the fire had been accused of the Connecticut Brinks robbery in which guards will killed and the money stolen to underwrite the separatist movement. They are a group that will never accept statehood.