These games could be crucial sleeper hits for Wii U. Could being the operative word, though.

Splatoon could establish a competitive scene and shake up their image by showing they don't just recycle old IPs. But as an unfamiliar property, it will need a push to build up a sizeable userbase; as has been suggested in the Nintendomination thread, aggressive advertising though Nickelodeon, Cartoon Network, etc could go a long way.

The problem is, will Nintendo be willing to give it the necessary push? Their marketing these days tends to be, well, awful.

Same with Mario Maker; given the current popularity of DIY games like Minecraft, plus the nostalgia factor of 8-bit/16-bit Mario, it could be huge. But it will need to be appropriately priced and pitched to the mass audience, instead of just Nintendo fans who watch Directs and follow them on twitter.

Nintendo needs to really step up to the plate and plug these two hard, or they'll fumble two critical opportunities to expand their player base.

They barely gave MK8 and SSB much of a push, cant see Splatoon or Mario Maker getting anything.
The way I see it, if its not on 3DS its not getting advertised.

Probably... Their marketing has pretty much been sub-par

I actually saw a good number of Mario Kart 8 commercials and also Smash, which I saw in the theaters no less. 

Their marketing has gone up since 2013.  Bayonetta 2 had commercials on appropriate channels, Hyrule Warriors had commercials on appropriate channels, Smash and MK8 same.  It's not spectacular, no, but it's a lot better.  We'll just have to wait and see; they're not consistent enough to make calls.

I don't expect any kind of mainstream advertising push for these titles

I would be sorely disappointed at the marketing team if Splatoon isn't advertised on Cartoon Network frequently. Nintendo doesn't have much to go on for the first half, so they really need to figure out how to show off their products and fast. The word of mouth won't be as effective in a world plastered with advertising.

Nintendo products stand out, but if they don't show how they stand out they won't get the sales they deserve.

I can testify that I saw a Smash commercial in the theater as well. I was pretty shocked.

I don't think they'll get a big enough push, but lately every Wii U game has gotten at least some sort of advertising, so I expect that.

Nintendo's marketing kills most of their products

I'd like to see some advertisements pop up on my words with friends saying "You could be playing a real game right now. Only on WiiU."