I think the only thing that would make it worth being a "premium feature" would be if you could have multiple accounts attached to one security box. [Where items in it would be available to each account attached to it, and you'd pay for each additional account.] Because we already have a secondary inventory box feature in the current inventory arranger. It doesn't require a second password, so there's no added security, but an extra layer of security is not really worth paying for. [Just make a really complicated password and never give it to anyone and you'll be fine 99% of the time. And that second password probably isn't going to help you with the 1% anyway.]
I thought they were looking for feedback whether it would be premium or not? Like over 50% of the poll respondents said they were interested in the feature but didn't have gcash for it, at least when I voted it was that way.