In this scenario, the 10% would be forced to exit as their deposit would be slashed, and would drop below the required minimum for a security deposit. So within a short period, you would end up with 50% signing on A, and 50% signing on B.
These would have to have different network or chain IDs to avoid slashing events. One of them, presumably B, would have had to actually change this number from whatever the previously standard/agreed-upon chain ID is.
I could imagine this scenario happening in a contentious split or attack, but it would create two very clearly different blockchains with different goals and needs, like what happened with Eth and EthClassic, or Eth and EthPoW.
These would have to have different network or chain IDs to avoid slashing events. One of them, presumably B, would have had to actually change this number from whatever the previously standard/agreed-upon chain ID is.
I could imagine this scenario happening in a contentious split or attack, but it would create two very clearly different blockchains with different goals and needs, like what happened with Eth and EthClassic, or Eth and EthPoW.