There have been a few, vague pieces of evidence suggesting that HBO Go would be coming to Wii U. However, it hasn’t been util now that more specific proof pointed to the possibility.
A Time Warner job posting states that the company has partnered with Nintendo (and others) who “will launch HBO/MAX GO in the future.” These services could potentially make their way to the 3DS, but a Wii U channel/application/download is more likely at this point. After all, the same job listing does mentioned “connected TV and game console digital partners”.
The relevant posting in full:
“The Partner Manager position is responsible for the day-to-day relationship and ongoing marketing activities with several key Mobile, Tablet, Connected TV and Game Console digital partners for HBO GO and MAX GO. Partners include Apple, Amazon, Google, Microsoft, Sony, Nintendo, Samsung, Roku, as well as any new partners that will launch HBO/MAX GO in the future.”
Perhaps Nintendo could make an announcement about this at E3. Or maybe they’ll save the news for a later date?