Some infos concerning the padlets
In a v4 dev kit context, with third-party involved, ports & titles using inhouse engines (not really tailored for the Wii U), the system hasn't the capacities to render 1 720p complex content on the TV, and 2 480p intricate scenes at the same time, with a good enough framerate. The "v5" dev kits won't change this situation. And i really don't think that with first-party, it will be a totally different outcome.
Now, 1 light 720p content (a ranking list, a 2D map, etc.) + 4 480 not ultra detailed with to-the-roof poly count titles, well, the hardware may handle that (i'm talking about rendering capabilities here, not streaming possibilities).