RIP what a hero. Anyone know of a replacement? Will these eventually stop working?

What do you want to do? You could try to Ppick a problem and then find a service to solve it. Maybe a pi hole ad blocker, or homeassistant for home automation. Both of these run well on a pi. Then follow the guide to deploy those services.

Dead internet theory?

Juse use easyoptouts. Way cheaper for same thing.

You already have a pihole. I assume you like it. You could buy a cheap minipc/NUC and set up proxmox on it and learn to set up and configure a second pihole as a virtual machine. Then you’ll have a server running with the ability to expand as needed. You could look into setting up new network gear (like tp-link’s omada) and run the software controller in a VM. Or you could dabble with HomeAssistant and get into smarthome. Or set up a photo management tool like Immich. Like others have said, find a problem you want to solve and use these tools!