A recent post has made it clear where the future of industrial scale spamming and scraping is increasingly headed. In short, exploitation of the nature of cellular phone networks is about to unleash the kraken in ways that existing countermeasures will all prove useless against.
Mobile phone networks are all essentially large proxies for fleets of NATed devices. As such, getting a new NAT IP is as simple as turning on and off the radio, and if you are moving around, likely a new proxy IP as well. That said you don't even need to move around, as blocking any IP from mobile phone providers is basically a nonstarter. Nobody wants to block the large number of legit clients coming from their IPs, after all.
One might think that eventually the telcos will wise up and start banning. The trouble is that the mobile nature of these systems and wide assortment of carriers to spread requests over make it entirely viable to be both mobile and decentralized enough to have no effective means of enforcement. To a large extent, I suspect we are already in the early stages of this problem given there are firms making hardware facilitating this.
Is the only way to resolve this problem would be to forgo NAT altogether and embrace IPv6? Not really, as IPs are so plentiful there as to make bans useless once more. Even AI and Bayesian filtering has proven to be insufficient at improving fingerprinting enough to matter. The only practical option left is QoS measures to ensure you at least don't get DoSed by this stuff. That, and actually improving the performance of your mailserver and web properties such that they can bear the load.