The reason that traits (like pearl eyes) have disappeared is because of dilution by other breeds. Crossing a different strain to fix a specific trait will add whatever dilution that strain contains. Breeds can become a cumulative product of their dilutions.
There are some people who have tried re introducing the original ingredients of the Cornish using oriental game breeds that have remained pretty pure since the time of the Cornish's invention. The examples I have seen in pictures from Australia and Belgium among other places, looked very nice, much like the old pictures of Cornish that the hatcheries put in their catalogs to avoid the embarrassment of using a picture of the birds they typically ship.