I use an iPad 4 with iOS 7 on it. Just for browsing websites, so apps and web apps are out of the question. For blocking ads, I run an Alpine Linux VM with dns

I use an iPad 4 with iOS 7 on it. Just for browsing websites, so apps and web apps are out of the question. For blocking ads, I run an Alpine Linux VM with dnsmasq and a massive block list. This VM masquerades as a DNS server. Last fall I had to install a Letsencrypt certificate to have more websites working. Lately I've been experimenting with Squid (caching proxy) to enable SSL bumping to get Wikipedia to work (they use TLS 1.3 and Safari 7 doesn't understand it). The experiment was successful, but I don't like how Squid behaves in other respects. So it is possible to squeeze some more life out of these devices, but they remain limited because of Apple tying the browser to the operating system.