The Short answer is yes.... eventually
Let me explain why.....
1) In the Original Wow clients Vanilla, TBC, WOTLK - these used locked opcode values for each packet sent between the server and the client.
Since Cata each patch randomised these values, thus meaning we would have to reverse engineer and work out the values for every opcode value for that patch version.
2) The Data structures are based on the BFa structures not the original Vanilla structures.
3) The nuClassic client would have to be 'patched' like all versions from Cata onwards, to use an ip address for the realm server rather than the Bnet server.
What this means is.....
To support the nuClassic client, it would effectively be a new core version of mangos. Not impossible to support, but that's a lot of work
I would also add that it will be almost impossible to play using the original Vanilla client and the nuClassic client on the same server (for the reasons mentioned in 1 & 2 above).