I suspect anyone who thinks landfills will ever be mined in the future has never been to a landfill.
If you want to recover metals from garbage, it's much easier if you burn it rather than bury it.
If you want to recover metals from garbage, it's much easier if you burn it rather than bury it.
With regard to metals, probably the biggest impact that won't happen on its own without consumer and regulatory pressure is to get the manufacturers to take back electronic devices and reclaim the metals that they use.
At that point there's various chemical methods to extract/separate metals from the plastic. Burning is possibly an option for the final remaining hard to disentangle parts but a few simple up front decisions can make items easy to disassemble for re-use in a standard 80/20 split.
One neat trick is to recycle batteries that are a mix of elements, but not bother to separate the elements, then sell the mix to someone who needs roughly that mix of elements anyway, like battery manufacturers. Saves time/effort and energy. Small additions can rebalance it.
I take the graph as being related to what percentage of the final item is that metal. If you make something that's 99% iron then recycling can happen more easily without up front planning than .01% gold mixed in with all sorts of other stuff.