Dumb for two reasons.
1. Clogs the network.
2. Cold storage. Most coins are in cold storage because people don't just randomly withdraw all coins simultaneously. So withdrawing all at once will be simply impossible because of the security measures in place that protect customers of exchanges.
In short, this looks like an attempt at a FUD attack. "OMG look these exchanges can't instantly withdraw all coins" and/or "omg look at how the BTC network crashed".
My thoughts exactly - "don't fix it if it ain't broken". Why in the world we would need this network stress test? Everything works as expected. Looks like an evil plan to sabotage
price and moreover could cause a dump. It's plain stupid.