Maybe not before, but i think he stays a lot better now than years gone by. I'd have little doubt him staying at least 3m4 with the assumption the ground won't be too testing. After all, I think the stamina required for a national is different than for other long distance races, and he has plenty of pace to be able to lie up with the leaders. After that, who knows, but a lot of people believe in the theory that you need a 2m5 horse who can hunt around for the first circuit - not sure I'd subscribe to that, but I believe he would have every chance of staying, plus has more class than almost anything else likely to line up. I'm not sure i've seen a horse jump better than him this season either.
I'm certainly not suggesting he should be in the top 5 in the betting, but I think there is a case fo saying he may run very well.