No, we wanted to create the best experience for the new extensions. We thought a lot about trying to be able to migrate the old extensions to the new site, but as we tried to do so, it became clear to us that the cost of that would be that the new extension would be a worse experience if we wanted to build a new extension that was backward compatible with the old system. We know this is inconvenient. This was a hard call, but we needed to make this compromise in order to build the new extensions on a solid foundation that can significantly improve the experience of using miniExtensions in the long run. Because of that, we decided to give folks the full ability to still use the old extensions as much as they'd like on our legacy website, but we also wanted to build a new site that can dramatically improve the user experience in the long run.
There's no one-to-one conversion from the old extensions to the new site. That's why any conversion we do would cause the converted new extension to actually not be the same as the old one. This would mean that the conversion tool would be creating new extensions that actually would not match the behavior of the old extension that the user had. Manually creating the new extensions is indeed inconvenient, but we feel that it's better than converting extensions to ones that do not actually behave in the same way, resulting in terrible consequences for our users. We know that this is not ideal and we apologize for the inconvenience.
Since the two systems are separate, extensions in the new site cannot be used in the legacy site and vice versa.