Funny you should start this topic, I too have recently been pondering how to bring waders for fly fishing without adding too much weight.
I was thinking though, instead of socks, etc. that you would carry in your pack, adding weight, and time to put them on/take them off.
How about designing a goretex/event shoe, that just has the goretex/event lining extend up to your hip? When not in use you could roll them down to the top of the boot and just hike like normal. Come to a stream crossing, or decide to do a little fishing at you lunch break, just un-strap/fold/etc. them from the top of your boot and pull them up to your crotch. They could be made loose to go over your pants and have a little shock cord draw string at the top to keep them in place, or even a little loop that would snap to you belt or belt loops of your pants/shorts?
Am I so off base with this idea? They already make waterproof goretex boots and trail runners. Would it be that difficult to just bring that liner out of the top of the boot? Of course, this idea is probably a little too involved for the average MYOG guy, but some of the more experience ones(especially with making shoes/sandals) might be able to pull it off.
Or should I just try and find a willing shoe manufacturer to pitch the idea too?