The term “the ten tribes” refers to the legend that the exiled tribes were lost, and will one day return. When someone uses the term that is what they mean. And the gemara says it’s a myth.
The most obvious meaning of the posuk is that there will be no more tribal rivalry. Right now that has been fulfilled; our tribes (whether we have two or twelve) no longer have separate identities, so there can be no rivalry between them.
However it’s also obvious that every Jew is descended in the direct male line either from one of the tribes, or from a ger. When Eliyohu comes he may well inform each of us of our yichus and we will know who we are. For those of us who are descended in the male line from the original Bnei Yisroel, he may also inform us exactly where our property is in Eretz Yisroel, that we inherited from our ancestors. So assuming that there remain at least some descendants of Efrayim, we may re-form the tribes. In that case, the posuk is promising us that the re-formed tribes will remain friends.
Either way, the idea that Sefardim (or any community, such as Ethiopians) come from these “lost tribes” is not feasible.