I'm no expert by any means, but it would seem to me there would be a lot more to lose (financially) than to gain. It has been mentioned that unlike here in the U.S. where a fish may be shown in different size classes over a period of years while it is still improving, that in Japan they are usually raised to a peak finish, shown, and ulikely to hold true championship form beyond the peak year. Taking GC one year only to come in a lesser place the next... That would imply a decline in prestige and perceived value. Owning a Champion is better than owning a has-been.
Current pictures of many famous Oyagoi are never seen. Faded glory in the pond doesn't change the quality of the offspring, but it could be a detriment in marketing them.
Just a thought from a rookie.