At the end of the day, third party support will depend on how well the Switch sells. If there are 50mm potential buyers of a game on Switch, then that game will come to Switch. If there are 14mm, like the Wii U, there will be a lot fewer games developed for, or ported to it.
I suppose there is a chance that if the Switch sells really well, devs could build games as Switch first, then port them to the more powerful PS4 and XB1. That could hold back progress across all systems. This seems pretty unlikely to happen widely though, as it would require huge sales among the correct demographics for it to make sense for devs to approach most games this way. It very well may be the case with games like Disney Infinity and Dance Central though. But, in that case, would we even notice?








