Why don't the main Halachic authorities (e.g. R' Ovadyah Yoseph, the Hasidic Rebbes, etc.) come together to make one Nussach for everyone; combining the Minhagim (e.g. Temani pronounciation, Yekkish fast days, lots of Piyutim, Hasidic Yom Tovim, some Sephardic leniencies, etc.)? It would create a lot of achdus - the kind of thing that got us the Torah.
Achdus does not mean we all have the same menu, Achdus means we care and lookout for each other.
Imagine a family where each member takes different medications and someone comes along and says 'why don't you have Achdus?' 'Get all your doctors together and come up with medications that is equal for all!'
The Achdus that got us the Torah in the first place was that all the Jews were one heart with each other without animosity towards each other and not that they all had the same taste in mind when eating the Mahn!