Because you mentioned the 12 outlet limit, I assume this is a Canadian Code question.
347 volt circuits are not permitted in residential installations, so the 12 outlet limit does not apply.
For commercial/institutional/industrial jobs, yes, you can use multi-wire branch circuits, and there is no limit to the number of lighting fixtures other than the normal circuit ampacity limits and the circuit overcurrent limits, where the connected load is known.
Ed
[This message has been edited by electric-ed (edited 11-13-2002).]