Accepted but I think the original claim was that plenty of horses prep (didn't necessarily mean final prep) over shorter.
This is an unusual circumstance and, presumably, not one Henderson would have planned. He's just trying to make the best of adverse circumstances.
I certainly don't see it as any big deal and the up side is that anyone who fancies Champ for the festival might be in a win-win situation here, in that if he just pops round near the edge of his comfort zone and loses (as I expect), his price will lengthen for the festival. If he goes and wins (which I can't see), it strengthens his case for the festival as it will show he has the pace for shorter.
Dick Hern once said Brigadier Gerard would win a Nunthorpe. Ruby Walsh often talks about the difference in pace at different trips being only about 1mph, it's sustaining the pace over the trip that separates the horses.
If they go anything other than a true pace over 2m, Champ shouldn't be too far, if at all, out of his comfort zone. He'd be likely to plug on at one pace in the final half-mile. If they go fast he can just sit off and plug on as the others slow down from the final fence and finish respectably held.
I have no financial interest in Champ for any race at the festival so no axe to grind. I just don't see anything wrong with the idea of running over 2m in the circumstances.
I dont think it does his Gold Cup chances any harm, and will run fine and safe. He will go at his own pace and may stay on if the race falls apart. I don't think they will be going quick enough to put himself in danger jumpwise, as the instructions will be for him not to get involved in anything that causes him any danger. Henderson is letting everyone know that he isnt really gunning for this race, and will be interesting in the circumstances to see how stewards and media cover it.