It’s been around for many years now and famously was used in the consultations for the constitution of Iceland. We also used it in Bulgaria back in 2013 and had a community of more than 3000 users, but it lost traction due to being ignored by politicians and controversial debates.
You can see more recent activity on https://www.citizens.is/ , particularly the impact and news sections.
https://github.com/CitizensFoundation/your-priorities-app/issues/161
It’s not a straightforward task. And it’s controversial is you want to avoid multiple registrations.