Yeah it's more than just an arena, but all this secrecy is stupid and will only make citizens su ious. It seems fairly likely that, after they got the federal courthouse and the ITC to move out, the city will try to clean house by getting the SSA, the Mexican Ins ute and the Universidad to leave as well. Then they could bulldoze everything except the tower and have a clean slate from I-35 all the way to Hemisfair Blvd. There will be plenty of room to place an arena, expand the convention center and build all kinds of other crap like housing, retail and hotels around them, maybe even a new Missions stadium. I bet there's even a plan to extend the extension of the Riverwalk. Then put in an even bigger pedestrian bridge (or some idiotic Elon Musk transport like Vegas) connecting the whole schmear to the Alamodome.
That's how you get a $4 billion price tag. It's going to be a series of glorious civic fights over the next decade.