Merchandise with the eeveelutions (Including Slyveon) is everywhere in Japan, the Pokemon store is full of it. Bags, books, pencils, hats, clothes, I doubt they would add another one to then have to re-design all the stuff.
I'm still hoping that there is a Dragon Eeveelution, for these reasons:
1. So far, new Eeveelutions have come in pairs: Espeon and Umbreon, and Glaceon and Leafeon. It'd be disappointing to see 6th Gen not continue the trend. 2. One of the paired Eeveelutions has a type advantage over its "partner": Umbreon beats Espeon, and Glaceon beats Leafeon. A Dragon-type Eeveelution would be a logical choice here, considering Fairy's advantage over Dragon, and would hype up the new Fairy-type as well. Alternatively, they could also introduce a Poison-type Eevee or a Steel-type Eevee (since those two are said to be strong against Fairy).
Though I agree that if there WAS a second Eeveelution, they'd be advertising it right alongside Sylveon. Unlike in Gen.4 where both of the Eeveelutions were unknown until the game came out.
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The issue with the "they would have revealed by now" argument is that Sylveon is special. She represented a new type not found in the previous games. Granted by now they should have revealed it, but still that could have been a factor and could be hiding.
However as of late they've really went away from the norm. I bet Sylveon is the only one.
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