Out of sight, out of mind.
It was a solution, just not a good one.
Arguably, in 1964, it saved little Johnnie from getting cut.
If I had room in my medicine cabinet to actually get to a blade slot, I might put one in...
It's a great idea and far safer than any gussied up procedure used today. idiots and Children can't get to the blades behind a wall. I doubt the space could be filled up in an entire life of any house. And, construction tear down is dangerous any time and all the time. I don't see any problems here?
What's wrong with it? I personally think it was a good idea, having grown up in a couple of houses, the first dating from the late 1940's, both having "medicine cabinets" with the blade slots. It would probably take several lifetimes to fill the cavity between the studs, and anyone doing a remodel would immediately see what was there, no more dangerous than a lot of other things found or involved in construction projects.