Thanks to a tip from a correspondent, I can confirm that there is now demolition underway at the ballpark
site, at its southernmost corner (South Capitol and P and Potomac). They are also "demolishing" (i.e., digging up) the triangle of empty land at 1st, P, and Potomac known as Reservation 247. Plus, now that the asphalt plant at Half and O has been dismantled
, they're also digging up and clearing that lot as well. And they are in the process of putting up more fencing around the perimeter of the site--looks like they will have O Street at South Capitol fenced off by the end of the day. So while there hasn't been any sort of official groundbreaking--and I haven't heard whether there will be or not--clearly they are now moving forward.