Within the last week on WDWMagic, a former CM named CSUFSteve started a new thread about having received a CM package back in 1997 showing DL's plan at the time for the DLR expansion that was to follow. He posted a link in his profile to a JPG showing a map of the resort area entitled "The Disneyland Resort Master Plan." It shows not only California Adventure, the Grand Californian, and Downtown Disney roughly as we know them today, but also what is apparently the next phase of DtD extending out towards Mickey & Friends and ending at what the map legend refers to as "Magic Kingdom Hotel" which is positioned between the existing Disneyland Hotel and Mickey & Friends.
Here is the original post on WDWMagic by CSUFSteve:
Here is the link to the image:
It's far from exactly what DLR is today, but it is roughly accurate. The most notable exceptions are the extended DtD and the Magic Kingdom Hotel areas which are little more than parking lots today. Could be a clue to the next phase.