I've seen plenty of people finger-farking-fones while eating so the idea of attaching a spoon to the smart phone makes sense. (Most smart phone users aren't smart enough to use a fork nor careful enough to be trusted with a knife.)

As to attaching knife blades, I would consider something like a male-female nut system, e.g.,...

https://www.alibaba.com/product-deta...897481361.html

or just an Allen bolt with suitable spacers sold with the blade.

I'm assuming that one wouldn't reconfigure his knife often so a bit of fiddling to do it wouldn't be a deal breaker.