You can find a lot of interesting topics on Sylveon on Tumblr surprisingly enough. I think I may be addicted to Tumblr now XD
Just a few of the things I found that warrant interest.
Like how the Flying one compares Sylveon to Skyla, this one compares Sylveon to Iris. Yes I have posted this before but I never went into detail about it before.
First thing to note, the creator of the image "reverses" the cycle on us. When we first got Eevee Circle image people created images "proving" eevee was Flying type as on one side has weaknesses. This one points out Resistances/No Effects.
Starting with Glaceon, Glaceon deals NVE damage to Flareon. Espeon deals no Damage to Umbreon, Vaporeon deals NVE damage to Leafeon, and Jolteon deals NVE damage to (Dragon typed) Sylveon.
It then compares Sylveon's Red and Blue stripes on its ribbons to that of the old 3rd Gen Dragon button. The final comparison is Sylveon to Iris' Champion Dress. Iris' Champion dress is roughly the same shade of Pink as Sylveon and has various ribbons and bows on it.
This one is all text so it pretty much explains itself. It is one of many of the original findings linking Sylveon to Flying type.
Another one linking Sylveon to Dragon type. Pretty much the same as before minus Iris.
This one relates to the "Love interest" in B2W2 if you chose to play as Nate. The young pop star has bows on her outfit much like Skyla and Iris. This one is a fan speculation relating Sylveon to a new type: Love. Considering Sylveon was released on Valentines Day, a feat that seems to have been done on purpose by TPC.
This one is just a fan drawing to show how Sylveon looks like a Ghost type to them. Quite creepy, which is really well done considering how cute Sylveon is.
There were two more, one relating Sylveon to the Forests and proving its Bug relation, though I cannot find anything on Tumblr about it AND one relating Sylveon to another new type speculation: Magical Type.
A lot of the rumors popping up are quite fun to read, but this is pretty much all I've gathered so far. There are many speculations based on name but since we are doing it from the fan basis with no official name referencing, its all hard to sort out fact and fiction. A lot are taking name to force a thought that Sylveon is female only.
Though anyone that really delves into he mythos to Sylphs and Nymphs knows that neither have genders and can appear as males as well.
With this, my personal stand point lies in Dragon, Normal, or Flying. Either of the three I'd be okay with, though I am posting them with personal priority. I do not subscribe to the female only for reasons I've posted here. I feel Sylveon will retain Eevee's 9 to 1 Male dominance ratio. (Yes its 9 to 1, not 8 to 1. Eevee is 87.5% chance for male and 12.5% chance for female. Rounded to nearest whole favoring larger half is 88% to 12%. Rounded to nearest 10th, Male leads 90 to females 10. Divided for simplicity 9 to 1.)
And to finish this~ My favorite Sylveon related picture: