Re: See what "Day of the Doctor" with Ecclestone would have looked lik
Moffat showed us as much of that regeneration as he was comfortable with showing without having the actor present. I'd have to find his exact quote, but that's why the regeneration from the War Doctor cuts away when it does.
I always assumed that there wasn't a script for "Day of the Doctor" with the ninth Doctor in it, but if they got as far as storyboards then there may well have been. This leads me to wonder if there's some validity to the rumors at the time that Eccleston agreed to appear, only to withdraw from the project prior to filming.
Maybe it was optimism on Moffat's part that he could actually get Eccleston to do it. I certainly held out little or no hope of it happening though I was a little disappointed when we didn't get to see the War Doctor regenerate into the 9th.
Moffat showed us as much of that regeneration as he was comfortable with showing without having the actor present. I'd have to find his exact quote, but that's why the regeneration from the War Doctor cuts away when it does.