With 0.12 and opt-in RBF, nSequence will have multiple uses. It can be used for locktime and now signaling for opting in to RBF. However, there is nothing that I could find that distinguishes the uses for nSequence. Spending a time locked output requires setting nSequence to less than MAX_INT but opting into RBF also requires setting nSequence to less than MAX_INT. By spending a time locked output, you would also be opting into RBF, which may not be desired behavior. Since using nSequence to signal a certain behavior will probably be used in the future, is there any plan to change nSequence so that the features the transaction is using can be distinguished? Perhaps something like version bits? 

Thanks,

Andrew