To be clear, I am not taking a side on their Jewish status in halacha, but as to whether what they practice and refer to as Judaism is really Jewish enough to be on topic here. Just because a group claims to be practicing Judaism does not meant their claim has legitimacy. Just as Messianic Jews and Black Hebrew Israelites would not be on topic, neither should Beta Israel, if they have different canonical texts and interpretations.
As far as I know Mi Yodeya accepts answers and questions that relate to traditional Judaism. Traditional Judaism (as I define it) means any strand of Judaism that has a longstanding, traceable tradition that goes back into some kind of antiquity. But for the case of Mi Yodeya I would propose defining traditional Judaism as having a traceable tradition into antiquity, and/or be a group of Jews who practice a type of Judaism that is the norm for a large amount of Jews.
By my definition I don't consider many strains of Kabbalah to be traditional Judaism as some books and modes of thinking only go back a few hundred years and seem to come out of nowhere. But obviously Kabbalah has become normalized and has spread to various communities to differing extents so Kabbalistic questions should be considered as being part of normative Judaism.
Defining traditional Judaism as either having a longstanding tradition or having wide acceptance within major Jewish movements would definitely filter out a lot of the "problematic" movements that I think worry many of us. For example, Karaite Judaism is a sore subject, but I (and Ovadia Yosef) do not consider Crimean Karaites to be legitimate Jews, as their community was not longstanding and we can't trace its lineage and customs and their customs can differ compared to the Karaite Jews who do have a longstanding tradition. This definition would also exclude questions or answers about Black Israelites or Messianic Jews as they are new movements that began within the last few centuries. Technically Messianic Judaism started thousands of years ago but the movement was cut off and almost all current Messianic Judaisms are not connected to early Messianic movements like the Ebionim and therefore shouldn't be covered on this site. But a Jewish group like Chabad that organically becomes Messianic even if it goes against "normative" Judaism? I think it should be covered on this site.
However, this definition would allow for Ethiopian Judaism to be covered on this site as Ethiopian Jews have been around a long time, and were known by various Jewish communities throughout the ages. They have been mentioned since Gaonic times, and the Radbaz speaks about them matter of factly even just a few hundred years ago. We as Rabbinic Jews also have a longstanding tradition with Egyptian Karaites, which is why Ovadia Yosef and many other Sephardic posqim treat the Egyptian Karaites very different than those from Crimea or other parts of Europe. We knew of the Egyptian community, we had contact with them, we intermarried with them (as the Cairo geniza proves), so to exclude Karaites or Ethiopians from this website for not being "Jewish enough" seems really problematic.
In short: As long as we are willing to accept traditional questions and answers about Judaism we have to accept that Rabbinic Judaism is not the only traditional type of Judaism that exists. And it is my opinion that all traditional forms of Judaism should be discussed here, even if the questions or answers deviate from Rabbinic Judaism. Here is a small list of groups that I think we should and could accept questions and answers from based on the definition I've set out:
Orthodox Judaism, Conservative Judaism, Reform Judaism, Sephardic Judaism, Ethiopian Judaism, Egyptian Karaite Judaism, Ehtiopian Judaism, Samaritism, Kabbalistic Judaism, Chabad Messianic Judaism
Here is a small list of groups that I think we should and could reject questions and answers from based on the definition I've set out:
Messianic Jews, Most forms of Christianity, All Karaites other than Egyptian Karaites, Black Israelites, Rastafarianism, Islam (unless it explicitly pertains to a tradition they received from Judaism, this does happen)