I have no dog in the Brickfolio fight (I never used it and don't care if it ever returns), but doesn't it seem like the next step should be you asking people if they would like this new idea that you have or to have their Brickfolio data restored? So far, there is PLENTY of evidence that people want their Brickfolio data, but zero evidence that this new secret idea is going to be of any value to anyone. Not working on something that people are clamoring for to instead work on something that nobody is asking for seems a bit backwards, no? Listen to your customer. No, they haven't paid anything, but they're still your customers.
I mean, at this point, can't you just provide everyone a CSV of their data and not keep the hope alive that the Brickfolio will ever be coming back? I get it, it's a free site, and a free service that was offered. But, at the same time, they just want to access their data that you already have. According to your past posts on the topic, you've stated repeatedly that all of the data is safe. So, just make it available to everyone and move on from this project that you clearly have no interest in completing.