No it should not be valid
This site already has a number of rules that new users find surprising. Thus, any rules or exceptions we make should provide enough benefit to outweigh the resulting confusion and need to link to meta posts.
The cost of allowing this comes in the form of surprise and consistency: generally nobody would expect that code which autocompletes to valid code would be considered acceptable, and we make no such allowances for other editors. I think the argument about this being surprising is relatively self-explanatory, in that nobody would guess that
print(input( would be a valid Python program. The problem with consistency would then cause us to question why if we allow the IDE behaviour of Excel do we not allow, for example, Python in "IDE X" as answers where the code is autocompleted. I think our current rule, that the code needs to exist in a file in exactly the way it is presented in the submission, is much clearer and will require less meta bloat than allowing an exception would be.
The rule we have about anonymous functions is similar in several ways to this proposed rule, but I believe the key difference is what is discussed above. Both of these rules allow for slightly more freedom in golfing and restricted source challenges, but rarely allow for anything of particular interest. However, what counts as an anonymous function is easily extensible between languages, whereas this rule about a particular editor's behaviour isn't.