Hi Hervé
I don't know the details of NDIS but it may basically be similar to the capability of allowing Ethernet (type) data transfer on various interfaces (serial, USB etc.) as well as Ethernet itself on an Ethernet interface. This is a guess but may be releated to your second question.
There have been some developments using TCP/IP over multiple alterative interfaces (serial/radio, WiFi, BlueTooth, ZigBee are example of possibilities) which effectively look like an "IP Interface", which is where the NDIS (type) part may come in. This meant that developments have resulted in multi-homed capabilities where multiple "IP Interfaces" that are connected can operate on a single or multiple IP addresses (sharing MAC or with multiple MACs) and perform routing functions between these interfaces (and filtering) or communicate with internal services (again configured to be on various IF interfaces / networks). Futhermore, the work has also allowed these "IP interfaces" (or networks or internal services) to be assigned to as VLAN or multiple VLANs. The result is a high degree of networking capability and flexibility over various interface types with very low overhead.
At the moment I am working on documenting these additional networking capabilities included in upcoming project releases.
This may means that the NDIS part is basically there. I never used this over USB but I don't see why it shouldn't be possible - transparent data transfer or a simple frame packaging would be simple (as UART projects have used, whereby CDC-class USB and UART interfaces are identical in the uTasker project). It also depends on the USB host's requiremenst since this may want a specific USB class to be used which may be more complicated to realise.
Regards
Mark