Or maybe it has 2 different evolutions according to gender. I read one leak saying that. I dont think is true, but who knows. That, or maybe salandits evolution is truly beautiful, but a dangerous beauty (and also seems to have to do with snakes).
All the women shown are beautiful and considered as such, but most are dangerous, even Medusa, was beautiful but was cursed by Aphrodite (or Venus, dont remember) for being so beautiful. In any case, Medusa was once beautiful, was cursed and became very ugly (so ugly she could petrify anyone that dared look her into her eyes: glare), going on a killing spree of everyone that tried to see her. The fox, according to what I read, is a spirit/demon that feeds on the hearts of humans in order to keep her lovely appearance (it seems that it could change form or learns some draining moves, dont know). Cleopatra was also considered very beautiful and was a powerful woman (being a pharaoh and all that), but the most interesting thing: she most likely died due to a cobra biting her (possibly indicating the design, or the "corrosion" ability, also: poison fang), this may or may not have been on purpose (indicating that salandit can poison itself being a poison type). The sirens have 2 forms: winged women with bird legs, and the famous mermaid ones (the picture provided ironically shows both, a mermaid with bird wings); in any of their forms they are beautiful semi-women that lure men with their voices (sometimes sleeping them: sing) to then rip them to pieces.
My guess for salandit evo is:
-Egyptian design. Maybe even cobra-like or similar to Cleopatra.
-Beautiful or attractive. Very likely women-like.
-Can get wings. Unlikely, but possible, specially if you take in account the 2 appendages behind salandits neck.
Edit: Ok, around 10 post before I completed mine, thats... a record xD
Well, like I said, I doubt they will reuse the siren theme if Salandit has it. Maybe it loses it's legs entirely and just becomes a snake. But like I said, I think we shouldn't compare them to Salandit.