Very interesting. I worry that if I use your cloud, and a lot of other people do, all of your IP addresses will get banned by all the big players. It will definitely be a fun cat and mouse game!
Related story: Way back in the day, PayPal was just getting started, and decided eBay transactions would be their perfect customer. The only problem is that eBay didn't allow scraping. So they built an entire proxy infrastructure to go around eBay's rules and scrape them.
It worked. It worked so well, eBay bought PayPal.
The side effect of this is that I got control of the PayPal proxy infrastructure since I was on the security team for both eBay and PayPal after the acquisition.
We used that proxy farm to scrape the rest of the web looking for fake eBay sites (because they would block traffic from eBay's IPs) and we had the guys who built it help us build proxy defense for eBay and PayPal.
So this could work in your favor, if you manage to constantly scrape a large target who might want to buy you. :)
That honestly sounds so fun! Who better to build your defences than your attackers ahaha
Tying into your concern, keeping IPs fresh and high quality will definitely be a balancing act as we get bigger. It'd be one today too if we were to try to offer super granular location controls because there's only so many proxies in X state, let alone X city. Currently, we get to aggregate & QA from multiple proxy providers, so our total pool is 300M+ IPs in the US and so far we've had a 99.95% rate of getting a fresh IP address in a session. So so far so good :)
As for that last point, I guess we'll see what the future has in store for us :P