Hopefully Old Sarum will be one of a very small number of stations making the decision to move to 8.33 before aircraft are required to be able to address the new channel correctly, and I suspect (but don't quote me) that the enforcement teams will turn a blind eye to such behaviour for another four-and-a-bit weeks. Indeed the conspiracist in me believes that the early publication via the AIS website may even be accidental.
I would expect the AIP (and therefore SD) to be updated on the first update cycle post January 1st, whereupon all aircraft are legally required to have 8.33 compatible radios if they wish to communicate with ground stations which have been allocated 8.33 channels. NORDO is the only other legal option, as dialling up 123.20kHz on a 25kHz radio when 123.205 is the published channel will be illegal, after more than a decade of warnings. Remember also that the deadline for ground stations (other than a very small number with exemptions) to be 8.33 compliant is only 12 months away, and even the exemptions expire within the very foreseeable future.