I remember sketching out the idea for something like this when digital cameras came out in the 90s. I'm surprised it's taken this long for someone to do it, seems like it would've made more sense back when everyone had film cameras. I always assumed there was some technical barrier I wasn't aware of.
There was one in '99 - $800 for a whopping 1.2 MP image [1]. It did not do well [2], although to be fair there were a number of issues with that implementation:
> The lack of battery space, the need to open the camera to change ISO, White Balance or any other image setting, and the need to indicate a crop in the viewfinder if anything less than a full frame sensor is used, are all difficult to get around, especially considering that this had to work in more than one model of camera. And that made the large assumption that many modern photographers would be willing to live without a rear LCD to check their images.
This product definitely looks like it would be challenging to design an manufacture. Without having seen this post, I wouldn't have imagined it would be possible to fit a sensor and associated electronics in the small space meant for film!
