It seems the Athletics are going to stay on the same site they play now, but possibly in a new stadium:

The NFL’s Raiders are in the final year of their lease at the Coliseum and are interested in building a new stadium at the site.

“We’ve provided for the Raiders. I don’t think the Raiders are really behind any of this,” Wolff said. “Their owner is a nice guy and I think he’s just trying to do what we’re trying to do, make sure that the other guy doesn’t cause the other guy any problems.”

So maybe they build as they did in Pittsburgh, tearing down one multi-purpose stadium to build separate baseball and football facilities on the same site.