How does SE plan to handle any DDOS (if one does happen) on early acces?

[Nezm]

These things actually happen to call attention to lax security, not because there is no defense against them and we should all just give up. The guys who did those attacks (Lizard I believe?) called both targets idiots and they were mostly right.

Hmmm awful lot of those lax securities which may be used lie in bugs found in the NW or Infra manufacturers equipment, which has little to do with the company using it.

Saying as such I believe LS used a route which only redundancy could prevent. Meaning your security choices are close the service down or, or have a complete separate infrastructure to re route to. And that's pretty much it.
From there they might be able to be handled reactively, but the service is already down.