The Bridge was to connect the two planned Pop Century resorts.
Originally Pop Century was to be split into two resorts, the Classic Years (1950-1990) and across the lake the Legendary Years (1900-1940).
Construction was started in late 2000 on the Legendary Years but was halted in 2001 following 9/11 with a few of the building outer structures completed. The buildings across the lake have sat collecting dust and weeds ever since.
However, Disney is now working to complete the 2nd resort. The Legendary Years theme has been dropped. It will now be called the Art of Animation resort. Most of the rooms will be family suites similar to those found at All Stars.
I assume once this resort is completed the bridge will be opened up so one could walk between the two.