Japan had a well educated elite, strong government, a fairly large middle class, and a highly skilled workforce. In the 1500-1600s period, it was very equivalent to the European states, while some aspects could be considered to be inferior, it was superior in others. Japan was well placed to modernize. Eithiopia wasn't.
Still, assuming a strong bureaucratic state was developed, a prolonged period of Western advisors could modernize the country somewhat. Perhaps not to Great Britain, France, German level, but to a Portugal or Greece level of development.
Ethiopia has large deposits of gold, platinum, copper, nickel, sulfur, and potash. That is useful, but it lacks the all important coal and iron for 19th century style industrialization. It does have a lot of hydropower potential though. We could see textile and handicraft development, but it'll be second rate industry compared to Italy or Japan, much less the bigger powers of the 19th century.
It would probably be advanced enough to keep its independence and perhaps even expand to control the rest of the Horn of Africa. It would be a regional power, not a great power. However, it might end up colonizing Yemen and controlling access to the Red Sea. If so, it will either need to be friendly to the British, or it's going to lose its control of Yemen.
Eventually, it'll be the model for the rest of Africa to develop and modernize since it'll have been the only African state to do so.
Assuming it doesn't implode anytime between its modernization and now, Ethiopia would probably be either a middle income country on the cusp of being a developed economy, or a developed economy. Probably somewhere between Mexico and South Korea in GDP per capita.