There is a new Diaspora Policy document that the Ethiopian government is circulating. In my opinion, the most important thing for this (or any other) Ethiopian government to do on this issue is to allow Ethiopians to retain their citizenship by opening the door for dual citizenship (constitutionally). This creates the necessary incentives for Ethiopians to remain engaged in events in their home country and to retain their Ethiopian identity even generations later.
Currently, the government has adopted another strategy (the Yellow card) to give certain rights to people of Ethiopian origin. I think there are serious problems with that path. To start, it essentially makes people report that they have adopted another citizenship in exchange for those rights. There is however no guarantee that these rights will not change or be taken away in the future. If the government decides to reduce or eliminate these rights at some future time, there will be no recourse to the individuals who have declared their new citizenship. This is a very big uncertainty.
Second, there is a large number of Ethiopians born to parents in Europe, the United States and elsewhere. Giving them rights of Ethiopian citizenship ensures their continued engagement in events in their country (and not just them, but their children as well). The bulk of this involvement is likely to be economic, technological and knowledge transfer, and the benefits are likely to be very large.
There is really no reason to not allow dual citizenship. It is a much less complicated course to take. It encourages the participation of Ethiopians in their country and the potential benefits (both to the individuals and the country) are very large.