The protection would come in the form of foam and plastic padding inside pitchers' caps, adding about half an inch to each side of the cap, and an inch on the front. ESPN has a video up on their site showing a few major league pitchers trying on the caps, and from a distance it would be difficult for fans to tell the difference.
The caps would be optional at first, but widespread adoption would likely lead to a new rule in years to come. Major League Baseball certainly isn't dealing with the same concussion PR-nightmare the NFL is, but they're still taking steps to allow their players to protect themselves.
Among the players interviewed, Yankees lefty CC Sabathia said he would wear the new cap, even though he's never been hit in the head in his illustrious twelve year career."You can never be too safe," he said. "Especially with the way guys are hitting the ball these days."
No word yet on whether any Red Sox pitchers will decide to take advantage of the new protective headgear - but I would guess the front office would support such a protection for their investment.