With more assertive diplomacy Italy might have been able to claim Libya years early, at the Congress of Berlin.
This would cut off Tunisia from the rest of the OE. France did not have Tunisia yet. Who would likely get Tunisia?
Would the Italians rule Libya from 1878 as a colony, or would they simply have occupation and administrative rights over the area, which would formally remain Ottoman (this was the arrangement that existed with Austria and Bosnia at the time)?
Could native resistance simply thwart any Italian attempt to actually occupy its new possession/protectorate? Adua in the desert?
If Italy secured the area from 1878 on, would it still even be interested in subduing Abyssinia? Would it have any reason to try to mug the Turks of territory again later?