Well...
Header adapters are not meant for PCs, they are there for specialized boards. There are plenty of those.
That USB to ISA adapter, why would anybody buy the reverse nowadays? There aren't many computers with an ISA bus, but there are plenty of old specialized ISA boards that would cost a fortune to replace.
About that DDR4 extender, I have a computer where the processor cooler inutilized a memory slot (stupid motherboard designers?). I just left it empty, but could have used one of those too.
And... Ethernet into M.2 is plenty of interesting. I wonder how useful can it be.