The only ones I can think of that even stand a chance would be :
Winning Percentage (season) (record is .947, Greg Maddux once hit .905)
Winning Percentage (career) (record is .717 by Spud Chandler, Johan Santana at start of this season was at 2nd place with .716)
No-Hitters (career [season, too, I guess, since a lot of it just comes down to luck])
Strikeouts (season) (Randy Johnson came within 11 Ks in 2001)
WHIP (season) (Pedro Martinez holds the record at 0.73!)
WHIP (career) (Pedro Martinez is 3rd at 1.02!)
Because of the 5-man rotation, I don’t think anyone is ever going to touch career or season Wins, Losses, Complete Games, or Shutouts. Career Strikeouts is an almost impossible stretch, but maybe if a Randy Johnson-like character can stay healthy for 20+ years. Still, averaging 200 strikeouts a season for 20 years is not even going to get you within 1500 of Ryan’s record!
Because of the modern hitting explosion, career and season ERA (1.82 and 0.86!), seem next to impossible. Even Pedro Martinez or Randy Johnson (who I think are/were the best current pitchers in their prime) never really approached the record.
I was really surprised that a modern pitcher actually has the record for single season WHIP. And Greg Maddux managed to score 5th on the list for his incredible 1995 season. For Pedro to be number 1 even in this juiced-ball steroid age, one might make the case that his 2000 was one of the finest pitching seasons ever. To be 3rd all-time in this era, could he also arguably be considered the greatest pitcher (when healthy) ever?
Or perhaps the modern era hitting advantages don’t actually help players get that many more hits, but instead turn more of them into homers? That may explain why WHIP records are still possible, while ERA is completely out of the question.