Unfortunately Squarespace are rather secretive around v7.1 just like they are everything else. For me personally v7.1 can't replace v7 without some big improvements to the header, like you mentioned secondary navigation.
It would be nice to get some sort of direction or even stability from Squarespace regarding what they have planned but we probably won't hear anything until their test is over. But I know that they do plan on supporting v7 for some time to come, they just can't guarantee new features will make it to v7.
It would be REALLY helpful to know what the roadmap is for SQS 7.1
We are looking at building a suite of new websites and love many of the features of SQS 7.1 but can't live without a few of the missing features (import/export, secondary menu).
I understand that you are in development with this platform but some high level best guesses around feature set, timing and what will happen with SQS 7 would really help.