If ending segregated mode is a show-stopper, then that would also apply to the NW runway option.
Communities under the current 09L and 27R approaches would lose any alternation respite and those under the current 09R/27L approaches, 50% of theirs.
AFAIK, with the north west (or north option) of 3 parallel rwys, the intention is to keep segregated mode on 2 rwys and mixed mode on 1 rwy at any one time. However, the rwy operating on mixed mode would be rotated so it wouldn't be the newest one on mixed mode all the time.
Respite for flightpath residents would be
reduced (from 50% of the time to 33% of the time), but not
eliminated.
Extending 09L/27R to operate it as two rwys involves the
elimination of segregated mode and alternation altogether, otherwise there would be an insufficient increase in capacity compared to the above-mentioned pattern.
As a result, there would be no respite at all, and that is why (apart from any technical or safety issues that may arise) it is a non-starter.
With 4 parallel rwys of course, respite for flightpath residents would remain at 50% of the time (despite there being more of them) as there would be no mixed mode required.
It's a good job that aircraft are becoming increasingly quieter.