I was wading through the netcode from D2X and noticed there are some provisions there already for direct TCP/IP games over the internet using a server, thus not sending UDP segments to a broadcast address and limiting playability to the local subnet.
There is even a standalone server that will accept and distribute segments from and to the players, which can compile and run without the rest of D2.
Now, I have only looked at the code, I don't have a C++ compiler handy at the moment. But I might try to see how this can be used to set up a tracker system and give D1X/D2X direct internet TCP/IP support.
Any input from those wading through the source welcome.