The first time I used the Manage Configuration form, I tried pasting in a PHP array directly but due to the line breaks, it wasn't correctly identified (...and I later read the bug report that the array has to be entered on a single line). I then learned that the keys shouldn't be quoted even if they are strings.
Would it, perhaps, be simpler if we would use "eval" in this case since access to this page is restricted to admin users? PHP developers would be able to enter the array by copying in what they require and eval supports the existing formats that we use, including the use of unquoted strings.
I've posted a patch to the issue, for illustration, at:
Additionally, I was considering the use of a substring comparison rather than the regular expression comparison to check if the user-provided string begins with the keyword "array" and ends with a closing paranthesis ")"  (see my notes on the issue).