If I were to buy a developer account now, would it be too late to be able to get the iOS 7 and be legal? I'm willing to pay for it if it means I can retain all my data when the public release comes.
OP if you pay the 99 dollars to apple for a developer account you will have access to this beta and any future ones for the year that your subscription is active.
That being said it is beta software so if you have no plans to use the beta for development it would be best to wait for the stable GM to arrive in a few months. It will be well with the wait.
As with any beta software there will be bugs, and your datas safety can not be guaranteed.
op I know what your asking and if your main concern is keeping all your current app data while running ios7 betas up till the fall I would say wait. It's not what the beta versions are for. I made the mistake with ios5 and only run the beta versions on my older devices mainly because I don't want to lose app data