I like "Slavianstvo" specially since "slava" (at least in modern languages) means "glory" or "celebration". Where in the old days, for example, my Serbian ancestors would celebrate one of the Slavic gods (a chosen deity), today, in Christian tradition, basically the same thing lives on - only instead of pagan gods, we now have patron saints, which we celebrate once a year (it can last for a number of days) and this whole thing is still, surprisingly, called "slava". Not to mention all the merging of old beliefs with Christianity.
I like "Slavianstvo" specially since "slava" (at least in modern languages) means "glory" or "celebration". Where in the old days, for example, my Serbian ancestors would celebrate one of the Slavic gods (a chosen deity), today, in Christian tradition, basically the same thing lives on - only instead of pagan gods, we now have patron saints, which we celebrate once a year (it can last for a number of days) and this whole thing is still, surprisingly, called "slava". Not to mention all the merging of old beliefs with Christianity.
The word "Slavic" or "Slavianism" does not derive from the Slavic word for glory but the Slavic word for "word". "Slavs" are "people of the word" (i.e. people who speak the language, i.e. the people one can understand). As a counterpoint, in Polish for example Germans are called "Niemcy", i.e., literally the "mute people" - because their language was not understood by Slavs.
I think it should simply be called "Slavic", like the religion of the Norsemen is called "Norse". Using neopagan terms like Romuva or Suomenusko only leads to facepalms from native speakers.
At least one of the Muslim sources about the Rus describes them as Christians before the official conversion date. They may have been lying since being Christian gave you benefits when trading in Baghdad, but its more likely that there was a mixed Pagan and Christian population for at least a century before everyone officially became Christian as that's how it worked in better documented areas.
Just came to say that fire breathing unicorn-bull thing looks awesome.
I'm hesitant to over-tribalize certain parts of the eastern Slavic lands, especially the people living around modern-day Velikiy Novgorod.