From my perspective the issue is not really about whether bhikkhus or bhikkhunīs should live together, but whether in general it is a good idea to mix the genders in a monastery. Attraction often takes time to develop, and the more exposure you have to someone the greater the likelihood is that you will be attracted to them. The attraction that develops over time is much more insidious and dangerous than the immediate sort of fancy, since it involves a deeper involvement with and attachment to the other person.
I recognise that people are different and that for some exposure to the opposite gender will not pose a problem. I think it is the case, however, that we are very good at underestimating our own defilements and the potential for getting sidetracked. I have no doubt this is one of the reasons the Buddha laid down fairly strict rules for how to deal with the opposite gender.
The model we follow here in Perth seems to work well. We have one monastery for bhikkus and one for bhikkhnunīs, being over one hour’s drive from each other. We usually come together once a fortnight, when the nuns come to our monastery to listen to a Dhammatalk. And sometimes a senior monk will go to the nuns’ monastery to give them a teaching. To me this seems to be a good balance. The nuns get enough support to get their community well-established, but there is little personal interaction.
I believe a fairly strict segregation of the genders is very supportive of monastic life. There are not many of us. We need to be careful to look after ourselves.