It's not new.
There has always been a list of IPs.
Have you not been to dashninja.pl?
Always been this way.
All DIP3 does is make the list deterministic, which has all kinds of positive effects,and no negatives that I can think of. If I could, you can be sure I would be getting called names by all the SJW clueless jerks on this forum for pointing it out those negatives, loudly...
DASH did suffer a DDoS a while back, and proved to be quite resilient in spite of most of the MNOs of the time have not taken any steps to harden their servers. They learned, sorta... MNs are now tougher than ever. DDoS isn't even worth trying at this point, and a fair number of MNOs are still clueless...
MNs aren't mere "full nodes." they do a lot more. While it does make them more tempting targets, it also makes them more resilient targets. In the DDoS event I mentioned above, about 1/3 of the network was taken out...
It had no noticeable impact to the end user.
While I agree that It'd be nice to disconnect the MNs fro the IPs, I'm not sure if there's a viable way to do that. Counter DDoS methods generally require the same data.
In spite of all the mental masturbation on the topic, the best weapon discovered so far is good old-fashioned iptables-fu. And even when this is completely failed, and 1.3 of the network goes offline; nobody noticed except the MNOs who ended up not getting paid, and justly so , for not having good iptables-fu.
All it did was prove that Proof of Service works exactly as intended.
While your argument seems to make sense in theory, we've already proven in real-world practice that the MN network is damned near bulletproof, and by far, the most secure and reliable distributed system thus far conceived by man.
I just wish they would DO SOMETHING WITH IT instead of let it rot on the vine for several years...