The members of the Nostalrius team have returned from their trip to Blizzard HQ last weekend where the discussion centered around the issue of legacy or vanilla servers. The meeting was attended by World of Warcraft project leads, PR members and community managers and lasted the better part of a day.
According to the post mortem report on the Nostalrius site, the impression that the visitors came away with is that Blizzard would like to have vanilla servers but reiterated the company's feeling that implementing such servers (and, yes, they do have the original code) would not be an easy or fast process. No definitive answer was given beyond the stated wish to see them as part of 'gaming history'. The build would require all the maps, data and models form Blizzard that similarly require server files and client files.
In addition to the technical aspects of releasing a legacy server Blizzard also needs to provide a very polished game that will be available to their millions of players, something existing unofficial legacy servers cannot provide.
Read the full post mortem at the link above.