How could one think about DDoS'ing something relaying on thousands of segregated nodes? I don't see any point in this discussion.
This is how Bitcoin XT was taken down. One small poll added possibility for people to direct hashpower if they support Bitcoin XT, and after day or two under DDoS'ing they surrendered and just served Bitcoin Core.
Bitcoin XT nodes were DDoSed as well, with one user reporting local ISP serving hundred people was so overflown with traffic, its custommers could not use internet.
The message was clear: anyone who does not follow Bitcoin Core, will be DDoSed.
If more pools + more people run full nodes at once then chance for this happening is smaller, but nonzero because 1000+ nodes is still vulnerable to be DDoSed.
But then if it happens again, Bitcoin Core and Bitcoin is not option for honest people who support decentralization and free ideas, not violence and criminality.