No, leaded fuel will continue for several years as they haven’t found a drop-in replacement that will work in the entire existing fleet, and the financial burden of modifying engines is too high for them to mandate the change. Some existing planes are approved to run unleaded fuels but not all.

But MOSAIC probably will result in more aircraft being announced that are designed to run unleaded fuel because you won’t have to use a certified engine and can use something more modern.