This is super cool and would be awesome for situations where your guests are familiar with QR codes. But from my experience the process would go something like this: Visitor: What's your wifi password? Me: No password needed! We have a cool QR code you can scan that will auto-join you! Visitor: Oh cool, how do I use a QR code? Do I need an app? Me: Nope, just point your camera at it. Visitor: Like .. .take a picture…
It might be only my bubble (of non-tech-savvy people), but recently I started to use QR code to share my WiFi and there was never such friction you described. I don't do it with a printed out image, but my phone has an option to share the WiFi via QR code. Also, modern phones have a direct button from the WiFi connection screen to directly scan a QR and connect to WiFi... This is a thing... and it's easier to use it…
I recently did this with a few (some more tech-savvy, some less tech-savvy) people and it seemed to blow their mind. I don't know if this is a commonly known feature.