Clearly the Switch isn't about power anyway and for the type of games we have seen so far they don't require a high performance level. I think the current high pricing and low battery life means the best upgrade will be a 100% compatible model based on a better fabrication process in a more compact size.
If there is a mid-gen refresh I think it may be a model that supports virtual reality with a 1080p screen. So the new type of games are VR only. This assumes VR gets mass acceptance and Nintendo want their slice of the pie.