Why would adding a new bunker to the 18th at TOC be a terrible idea?
1. It is very good hole as it is.
2. The idea of adding a bunker reflects the modern assumption that adding features to a hole will automatically make it better. There is no reason to think that is true. Sometimes adding features will make a hole better. Sometimes they won't. Sometimes they will make it worse. When you are starting with a good hole, you have a high hurdle to clear to make the case for new bunkers or any other new feature. I see no reason to think that hurdle has been cleared re: the 18th at TOC.
3. We have been down this road before about changing TOC and our betters said "no". In 1926, as part of the Crane brouhaha (Crane did not like TOC), the major Golden Age British architects were surveyed as to whether TOC should be changed/updated. To a man, they said TOC should not be changed in any way. We are talking Colt, Fowler, Simpson, Alison, Abercrombie, Croome, MacKenzie. (See The Field magazine, 1926.) Me, I am happy to defer to the architectural opinions of that group. Peter Dawson thinks otherwise. I believe Dawson is badly misguided. (A modern day example of hubris comes to mind.)
4. TOC holds a unique place in the history of the game in general and in the history of golf architecture in particular. We had lots of talk about this back a couple of years ago when Dawson made his changes. All the arguments then about the special status of TOC apply with equal force to its last hole. I don't have the time to rehash those arguments here, but since about 1905 (until Dawson weighed in, that is) TOC was not been changed in any material way. The course functions something like a founding document for the game. It is the measure against which the practise of golf architecture is still measured. You should not - just because you think you have a really cool new idea - mess with that measure.
I could go on, but need to go play a bit of golf with my wife on this beautiful spring day.
Bob