A major mixed-use development planned along East Riverside Drive in Austin is getting a dozen acres bigger, and the project's cost could top $4 billion, its developers said Monday. Initially known as 4700 East Riverside, the project has been rebranded with the new name River Park. It is expected to be built in phases over the next 10 to 20 years. The development, which has drawn opposition from some residents and community members, is increasing from 97 acres to 109 acres, with plans now calling for more than 10 million square feet of new development. Its developers said the cost at full buildout will likely be more than $4 billion, based on 2020 valuations.