Hi Geordie !
In my opinion, one day decathlon can't replace decathlon as we know it since 1912 (the 3 days of Stockholm first olympic was due to the large number of athletes).
It was contested during the American championship til 1931 I think, and at that time, the world best performance were realized (Fat Elkins 1927-1928, Mortensen 1931).
Today, since 2013, int the city of Arles, France, André Martre renews the experience with good athletes, 8000+ (Bastien Auzeil, Jeremy Lelièvre).
As one hour decathlon, one day decathlon is a very good training in the beginning of the season. It allows you to know your real shape and preparation.
But decathlon is a two day competition; Why ? Because, if you run and jump and throw only about a quarter of an hour during 36h of competition, that's to allows you a good recovery between each of them. That allows you to begin a new event as the first one and in your best shape, to be at your best level.
During decades, the decathlon was too criticized by number journalists and observers, because one saw these athletes like "medium in all, good for nothing". We love decathlon because Ashton Eaton can beat the best hurlers or the best jumpers of the world, too.
If your performances in 400m and 110h and 1500m are poor, and the others events middle, because you are exhausted bu the quick decathlon, wher is the fun, wher is the display ?
But I agree to create two new events more (with nationals and WR and international contests) wiche are : one hour and one day décathlon !
If you read french, you can find on my blog this article : https://decapassion.wordpress.com/2015/04/25/combi...
And excuse me for my broken English