This has been discussed since he retired this week and he may have good case. I will borrow some of what I put in my entry a few weeks ago about Bunning called Does Jim Bunning Belong In The Hall Of Fame?
Click on this next ink to see where Schilling ranks in strikeout-to-walk ratio (relative to the league average) for all pitchers with 3,000+ IP. He is 2nd to Mathewson.
I found the best fielding independent ERAs since 1920 (an imputed ERA based on walks, strikeouts and HRs with HRs being adjusted for park effects). Schilling ranked 7th among pitchers with 1500+ IP. The list went up through 2005. He is now over 3000 and my guess is that he has not slid too much since then (he was not on the 3000 list yet after 2005).
I found that he was 44th in Park-Adjusted Pitching Wins Above Replacement Level. I think that was also through 2005. He has probably moved up several slots since then.
So he has some impressive ranks. I would like to have seen a consecutive 3-year period in there that was Cy Young worthy. 2001-02 are in there and 2004 is but he missed alot of 2003, which was a great year for about 160 IP. He still finished 7th in runs saved over average with park adjustments. In 01, 02 and 04 he had 20+ wins, lead league in K/BB ratio, winning pct over .750, 2nd place in runs saved each year. Had a 1st, a 2nd and a 3rd in IP. Not saying he should not be there. But if he had pitched a full season in 2003, then he is a no-brainer. I guess I am 90% for him (or so)