Actually, these things are still built on the current E-Series chassis, which has been around basically unchanged since fax machines were still commonplace. Most are build on the E450 chassis, but the E350 is still available. These are still available with the 6.8L V10 gas engine, as well as the 6.2L gas engine from the F-Series Super Duties.
And these vans aren't going anywhere any time soon. At work, we've started getting our 2021 E450s in, with the 16ft Transit Classik aluminum cubevan bodies. We order literally hundreds of these each year. And we have our initial orders placed for the 2022 E450, also unchanged.