I have already given a detailed response to this proposal here: Resolved: Insert "!" is a bad fixit - #98 by Geordie_J so I’ll try not to repeat myself too much here other than to say I am strongly -1 on this.
To me the actual problem being addressed here is legitimate: that force unwrapping and optionals generally are difficult to understand for a beginner.
The solution proposed here doesn’t seem to be adding anything of value though: every !! “Explanation text” in the proposal has been a case of documenting “what”, rather than “why”. I understand this as a “commenting poor practice” 101. In every case it’s obvious that e.g. “such and such was not a subclass of x”, but how does that help a new user of the codebase at hand, or a new user of Swift?
The issue with force unwrapping is that it should really only be used when you don’t know why the unwrap failed. For everything else you should probably be writing something more explicit (with a guard else fatalError or similar).
The fact that force unwrapping is suggested as a/the fixit is the real issue here. Obviously it shouldn’t be, provided you can give a reasonable explanation why the value may be nil (in which case there are alternatives: ??, and guard else).
Optionals are confusing and we need better diagnostics and more reasonable fixits, but adding yet another operator to the mix is not the best solution to this, IMO it is not even a “good” one.