I figured the OAC was a done deal after the city council inexplicably went along with BART's plans, but according to Living in the O, BART is under a civil rights investigation by the Federal Transit Administration. In part, this is because BART's EIR (Environmental Impact Report) is based on 2002 data, the OAC including multiple intermediate stops (the OAC plans currently have none), and a $2 fare (the OAC plans currently call for a $6 fare vs. $3 for the current AirBART). The cost for implementing the OAC will also likely be borne in part by higher BART fares and/or reduced service.
I've noted before that BART could build a new station at 98th to better serve the residents of East Oakland and implement TransForm's proposed RapidBART bus plan with intermediate stops for a good deal less than the OAC's $500 million (and climbing) price tag. This won't necessarily stop it, but it's a huge step in getting others to take a look at some alternatives.