Yeah, the usual approach here is to offer a free VPN service, and then piggyback traffic over the user’s internet provider. Much, much more scalable and cheaper than offering to put GPUs at a user’s home.
Wow, that's genius. Basically, user gets a VPN but so does provider, in a sense.
You can offer them a free anything, really. It's a pretty convenient way to pay, that mostly doesn't affect the user at all (unless their connection is very slow), but generates value.