As far as I know, the chain can't be DDoS'd like that (I don't know much though in this area) and the DDoS in the past has been on the interfaces only (Steemit.com). Essentially, since it is a controlled experiment it could be stopped immediately dropping the load to normal instantly.

I have no issue with it being trialled on the testnet before public trial at all however. I should probably have been trialled many times already but as far as I know, it never has been. the testnet hasn't been up that long though.