I'm more confident about predicting Xenoblade and Yoshi sales than Splatoon, because the latter is an unknown so it could potentially do really poorly or it could potentially strike a chord with people and sell like hotcakes.
I don't think Yoshi will be the biggest seller, though, although the ridiculously cute yarn Amiibos will help. Xenoblade seems like it's got a fairly substantial amount of hype behind it, and at the moment it looks more likely to launch closer to Xmas than Yoshi, which may help (depending on *how* close to Xmas it comes out). I think both of them will sell well, though; they should clear 750K-1M fairly easily within their first couple of weeks, and I expect both to pass 1.5M lifetime.
Splatoon could land pretty much anywhere. It could bomb, or it could be a system-seller. I could see it getting the right word-of-mouth and racking up Mario Kart-like sales because of how unique it is. I could also see it reaching only a very niche crowd, selling 100K in its first week and then disappearing from the charts.
Tentatively, I'll guess lifetime sales as...
Splatoon: 2M (I might be a bit optimistic with this).
Yoshi: 1.8M (the console's a bit spoiled for choice with platformers already)
Xenoblade: 2.5M (off the back of a Xmas-ish release, lots of fans carried over from the Wii/3DS and the way it's done well on most-wanted polls)
