I haven't seen any quotes about the weight of the new 7.3. But for reference, a 7.0L LS7 weighs around 450lbs with all aluminum construction and a dry sump oiling system. The Ford 7.3 has a cast iron block and traditional wet sump. I'd be pretty surprised if it's under 500lbs.
That may not be a ton more than a regular RBV V6, but if I were going to the trouble of a modern engine swap into a lightweight 1st or 2nd gen Ranger, and then removing a couple hundred pounds of I beam, cross member and radius arms, I'd want a lighter engine too. The biggest reason that I'd consider a swap like that would be to reduce unwanted weight and improve the balance of the truck. I don't need or really even want 500+hp/tq in a Ranger that weighs 2500-2600lbs. A turbo Duratec that weighed 250lbs and made 350-400 would be an absolute riot in a chassis that lightweight. But that's my particular dream build, and I know plenty of others would take the big engine and call it a day.