I think with Nintendo and their track record 900p is very likely. Also if you look at their scaling of handhelds, the next one up in power would be about that of the Wii U. I think the people who expect Nintendo as a company to make a machine on par with the current gen are fantasists as the Iwata era track record speaks for itself and this is essentially his final console. They aren't going to retool it at the 11th hour.
My firm belief is Nintendo will try and keep their handheld development relationships with 3rd parties and make a handheld which scales up onto a TV. This makes absolute sense for them as they could develop twice as many games as a first party for a single handheld unit (and sell a home unit as a secondary peripheral) and likely port Wii U games across ontop of that just at a slightly lower res and with worse textures if space is an issue.