There is a difference between operating lines independently to
deliberately making them technically incompatible so that even things
like rolling stock transfers to balance changing demands are impossible.

The only good thing is that maybe these other two lines will get an
automation that can properly drive the trains unlike the 'bang-bang'
controller Alstom has on the NW metro.

I still can't see the justification for making the airport metro 25kv
AC. Short route, short trains. The route is sufficiently short that
having 3 phase breaks to balance the load will be an issue, so they may
have to go to 'converter' substations that take 3 phase from the
distribution network, turn it into DC and then into single phase AC for
the overhead. Then each train has to take the single phase AC, step it
down, turn it into DC and then feed it into a VVVF converter to make 3
phase for the train motors.

Will the extra complexity offset the 'transmission efficiency' of the
25kv OCS ?

I'm waiting for some one to realize that automation could be applied to
the double-deck stock too. Not to many more years till some one realizes
the ETCS upgrade for Sydney trains is a precursor to GoA4 on the
'conventional' network. The union will not be impressed, but by blocking
DOO they have made the case for automation stronger.