After reading FAQs I thought It could be related to this site (ServerFault) but got downvoted and put on hold.
Because it's R&D, it falls out of the "production system" requirement. But it's a problem I ran across for my job, using solely existing building blocks (iproute2 & linux 3.10).
My question is (was): Macvlan based interface pings from host but not from namespace
I won't speak for any of the people who actually closed your question, but I suspect it had a lot to do with your use of VirtualBox.
There has historically been a lot of negative feeling toward VirtualBox here, much of it motivated by the fact that despite Oracle's claims to the contrary, it is not actually a Type 1 hypervisor and is not considered very well suited to running anything even remotely important.
As a result, questions involving VirtualBox almost always get a strong negative reaction here.
The remainder of the question seems interesting enough; network namespaces are probably going to be an important tool in the coming years, with so much of what we deploy likely to become containerized.
