Ethernet (at least oveR twisted pairs) is a full duplex transmission medium, so two devices should be able to more than saturate the MOCA broadcast network.
Additionally, >1Gbps is starting to become common on consumer hardware.
Again, it is probably not going to be a concern for most home networks, and MOCA should still be better than mesh networks or powerline ethernet.
I suppose in theory, yes. I'm not sure how often, in my home network, I would have full duplex 1Gbps transmission, unless I've accidently caused a loopback.
