To me, with regard to the initial list, the big question is what counts as a "classic." Personally, while I appreciate the quality of his books, I would not put Louis Penny on a list of "classics." I would consider him to be "contemporary" and once you open up the list to current writers, all hell breaks out.
That having been said, the big problem with what I just wrote is that Donna Leon and Jo Nesbo are on the list and they, by my score keeping, are contemporary writers. (To some extent, the same could be said about Umberto Uno and Reginald Hill, although they are currently less active than the two I mentioned at the beginning of this paragraph.
So... if I were king (okay, nobody is going to what that), I would kick Nesbo and Leon off the list and include Dorthey Sayers, and, (hmmm, tough choice) Dashiell Hammett or P.D. James.
PS - I have read six of the books on the initial list and nine out of the ten authors. I have never read a Rex Stout, but at times thought that I should read one of his Nero Wolf books.
PPS - Two famous writers who might be considered "classic" are Ellery Queen (actually I don't think he was a single person, not sure) and Earl Stanley Gardner. I have read both, and, to be quite honest, I consider their books pretty bad. They would not stand up to contemporary standards. The other authors still read well.
PPPS - What about Georges Simeon (Maigret)? Interesting novels, but more atmospheric police procedurals as opposed to mysteries.