I'm not sure why you think that is unlikely. I fully expect a 64 or 128 GB version sooner or later as memory and the other Wii U components get cheaper. It is not only a way to get people who scoff at the 32 GB (or less) to potentially buy in, but it is a "nice" way to get people with older Wii U systems to upgrade. I'd even consider it if there was a cheap upgrade path (not provided by Nintendo but say via a Gamestop trade-in promo). For example, I bet a lot of hardcore Nintendo fans would upgrade to a Smash Bros. edition system with special colors and more memory. I don't necessarily expect the higher-capacity systems until later years, though. But it seems inevitable.
I only have one of the "freebie" games (Pikmin 3) that come with Mario Kart 8 and will probably get one more (Wind Waker). I actually held off even bothering with the other 2 since space is limited and I didn't want to deal with setting up a USB drive. Besides, I already have NSMB and Wii U Party on disc (the latter still sealed). If space was not an issue, though, I might have tried to get a few more Mario Kart 8 codes just to have those two games on the system.