Ok this is not 100% true either. It wouldn't be too difficult to add a layer on
top of the nic hw emulation that did ethernet frame to ip frame and vice versa
before passing the frames to a tun device. (The user mode networking code
already does ethernet frame conversion.) So it wouldn't be that difficult to
get to work, and you wouldn't lose too much either (only IP-based protocols
such as TCP or UDP would work, but I've never heard of anyone trying to use
IPX or even IPv6 with qemu so that probably is not an issue).