Question

Would it be possible for more states to be added in the future?

Answer 1

Answer: it is possible

Explanation: unless otherwise it is rejected by Supreme Court? Or by congress?

Answer 2

There are generally three possibilities for the US to add new states:

Breakup of an existing large state
Conversion of an existing US territory into a state
Annexation (voluntary or not) of either another whole country or part of one, and then conversion into a state.

so yes therefore it is possible