Earlier quoted context omitted.
> When our 9 month old started to sleep through the night (at around 4-5 months), we'd get between 5-6 hours of sleep, which after the interrupted sleep of the previous 4 months, felt like a full night's sleep but this is sleep deprivation territory, specially given the fact that it was 7 days a week. Assuming you have the space for it, I never understood couples that insist on both parents being woken up every night…
I'm not a parent so my knowledge here is pretty scarce, but what I've understood from friends that have kids, is that when a baby wakes up, both parents wake up due to instinct (i.e. is the baby ok?). So I wonder if what you suggest would require some accomodation. E.g. have the 'on-call' parent sleep in the same room as the baby, and the other one can sleep in another room with the door closed. Is this what you mean…
> Is this what you mean by saying that both parent need not be waken up? or are there some other methods that would help out with this?
That's what I meant by "Assuming you have the space for it...". If the baby is in a separate room and there's space for a bed or mattress, whoever is "on-call" stays there and the other parent gets an uninterrupted nights sleep. Or the reverse and the "resting" parent goes and sleeps on the couch. 7-8 hours uninterrupted on a couch wins over repeated interruptions on a bed.
Same system works if you have a grandma visiting to take over for a night. There's no merit badge given out for everyone being equally sleep deprived. It's just worse for everyone, including the baby.
If the mother is directly breast feeding then likely she's going to be taking the heavier end of this load. If the baby is formula fed or she's pumping, there's more leeway to switch off.