So I threw this idea out there in a PTC thread but now that I think I'm serious about it I'm going to make it's own thread.
As a thru-hiker on the PTC I noticed that it looks like a good portion of the trail is just dirt trail (and in some cases even flat dirt road like next to the aqueduct). So it occurred to me that instead of carrying 30+ pounds of gear/water why not just carry absolutely no weight at all and have it roll behind you. So here is what I'm thinking.
Buy an external frame back pack. Solder two lawn mower wheels on the top of it. And then on the removal hip belt just attach a leash on either side. That way when you want to carry it the wheels are just sitting over your head without you even being aware of them, but when you don't want to carry 30 pounds and would rather just walk with no weight then you can set it down, remove the hip belt and just walk with it behind you.
Look at this Kelty external backpack and see what I'm talking about. It would require not much work at all to turn it into something you can just pull for thousands of miles instead of carry. It could save the hiking life of someone with bad knees too.
https://kelty.com/yukon-48/