The downsizing problem is the lifetime of stuff people acquire and what to do with it. While living it is their treasure, when gone it is someone's junk to get rid of and there is a lot of it.
The other problem, a bigger one, is some of us wait too long to downsize and by then we just don't have another move and all that goes with it in us.
There is probably a business opportunity for someone that can figure out how to efficiently and respectfully go through a life time of stuff and dispose of it but not in a landfill. Recycle and repurpose would be nice. After that someone would take care of all the relocation arrangements. It would be nice if there was an option to move into a downsized neighborhood that is not a ghetto but instead a single home retirement community with option for extended care / help. Dell Web is not the answer for me. If it is a problem and money can be made someone will figure it out. Money is the problem though. Capitalists want to make arbitrage level profits all at once then spring for the exit and the next boondoggle.
I think the Salvation Army will pick up stuff. I was helping my sister keep on eye the movers while boxing things up and putting them in the truck. She didn't want a few pieces of furniture so the movers called someone to come pick it up.