Iwata has said that it will and for reasons stated by Netyaroze, it's highly unlikely that it wouldn't be. Even a moderate power increase over the Wii will mean the console is capable of HD and if they aren't going to go for a moderate power increase then why bother releasing a new system.
I understand Nintendo's stance of not wanting to put technology and graphics or the forefront but actively discouraging it's use is different and having a new system released in 2-4 years that didn't do HD would be a case of the latter, not the former.