The following info comes from the Full Indie Summit, where Nintendo's Dan Alderman took the stage...
- no concept approval process for eShop
- no mandate to use motion controls or GamePad features
- Nintendo doesn't require platform exclusivity
- platform exclusivity for eShop titles was called "childish"
- interested devs can visit a special Wii U developers page and fill out a small questionnaire to work towards acquiring a license
- Nintendo will provide the Unity Pro 4 engine at no additional cost
- you need business entity status, which costs less than $200 in the US
- no hidden fees for devs on the eShop