I'm starting to suspect it won't.
They seem to always select low resolution screens for their portables; the DS was 256x192, (main screen only) and even the 3DS, at 400x240 (not counting 3D, main screen only) actually has a lower resolution than the PSP; if this trend continues, their next one may likewise be below that of the Vita, which boasts a sub-HD 960x540.
I know 720p screens aren't exactly an expensive rarity these days, but given the cost-cutting measures Nintendo has adopted for the last two generations, I can see them equipping their next portable with a 480p screen or thereabouts, which would also mean they'd need a less expensive and power-hungry GPU to render at that resolution, thus not only lowering production costs but extending battery life, which in a portable is crucial.
But enough of my jibberish, what do you think?