If I decided to do this, I would need to operate my LAN like every node was bare on the internet. I've got fileservers with guest access (for, you know... houseguests), web services, my invoicing system, and a whole slew of other personal services. The thought of open wifi on the LAN kinda scares me from a security perspective.
Um. My router has a 'guest network' with a separate SSID. Many free-from-your-ISP routers now do. For a tech news website, there are an astonishing lack of tech solutions in the comments here.
Promising costs nothing, it's the delivering that kills you.