Your forget about the Suez since the Ethiopians have no navy. Same for direct action against Egypt. Now the action is very likely to cause extreme concern in the UK. And how it plays out depends on the UK. The UK can really just ignore it besides maybe another division or two in Southern Egypt, Sudan, or Ethiopian coast ports. These don't have to be great divisions, and you probably have just a minor effect on the war. One of those, the war last 3 weeks longer type ATL no one likes to write. Or the UK can try to take Ethiopia. Ethiopia is a big place that can just absorb a divisions, even corps. It is a big logistical strain to get supplies deep into the interior. And then the question becomes "Where did the UK get these 4-12 divisions from. Wherever this is from, it is a big win for the CP. Cancel Gallipoli, and you get wonderful butterflies for the Ottomans. Pull them out of Flanders one division at a time, and German does better in many different ways. For example here, major UK action in Ethiopia probably solves (partially) solves in the west that stopped the 1915 offensive versus the Russians. Here, it will be a longer campaign stopped by winter. If the UK goes big into Ethiopia, there is a good chance the CP get a win.