I think its a silly idea. We already get discounts and free online. What could this service add besides 'free' games? Besides if they are going to flood their user base that already buys games with these bonus games it would be destroying their own user base.
Wii U owners actually buy games. This has already been shown time and again. The only way this would fly is if it is only for non first party games. Even then people will complain that it doesn't include Nintendo games because that is what people want.
Plus most Wii U owners would not be prepared for this system. Almost everyone outside of the hardcore do not have a external HDD attached to their Wii U. Nintendo floods the market with free games and people will eventually run out of room. Especially if they consider adding old Wii games to the mix. The way it is now, people pick and choose what they want, there is decent game sales, and games do go on sale when in the last gen they did not.
Mind you I'm not saying that a premium service should not happen. I just think that there are better options available.