If the standard of acceptability for the risk assessment is that there would be no more risk faced than if the lift were "compliant", then it's fine. The problems will come if someone thinks this means you can discount all the good stuff that BS 9999 recommends on the basis that there probably won't be a fire that knocks out the BMS; the lift controller(s); the power supply(s) etc, etc...
I think what this is intended to achieve is to allow the use of "normal" lifts remote from a fire for evacuation - e.g. if they were a two ends of a large building with suitable compartmentation separating them, such that if you have a fire you can treat one end as a protected area relative to the other. Airports might lend themselves to this, for example. You can then dispense with the small, protected refuges etc, as the whole of that end of the building becomes a protected refuge. What might be missed is the potential for a single fire to knock out both lifts - their power supplies or control systems - so that's a crucial matter for the risk assessment (and probably requires detailed technical analysis). I've also heard of problems with lift engineers agreeing to install the over-ride functionality on the basis that because they're not "compliant" evacuation lifts it compromises compliance with BS EN 81 & their Notified Bodies won't sign them off.