Block II SLS is the final evolution of the SLS rocket. Using "Dark Knight" advanced SRBs, the rocket can carry 130T to LEO- however, the Block IB is intended to become the "workhorse" of the SLS for the near future. The Block II, on the other hand is expected to come online by 2028-2030.
With SLS lacking money for payloads, the cancellation of Block II could free up money for a payload. However, the production line of the Shuttle SRB segments have stopped, so there are only enough for 6 SLS flights- at the minimum launch rate of 1 per year, the rocket would run out of boosters to use by 2026- leaving a launch hiatus of 2-4 years- a situation made worse if the rocket launches more than once from 2021-2028 in a year. Cancelling Block II would mean creating "drop-in"replacements for the current SRBs.
So should/can NASA cancel Block II and use "drop-in" Shuttle SRB replacements, or would it not save any money (even though the new SRBs require new aerodynamic models and R+D?)