On the subject of purchases being locked to the NNID: according to the Giant Bombcast, that does not appear to be the case. They claim that, with two NNID's on one Wii U, both accounts can play games purchased by either account. Which would indicate that purchases are not locked to accounts, but to the system. They're obviously associated with accounts - Nintendo clearly has a purchase history - but the NNID account is not required to be signed in to use content on the console. Very odd.
I haven't tried this myself, but I think I will tonight. I'll create another NNID and see if, when signed into that NNID, if I can not only play the games I bought with my real account (most likely yes), but also whether I can see my real account's purchase history (most likely no).
It seems as if nothing has changed, at least not functionally. I suppose it may allow things to change at some point, but they should have changed now, during this transition.