I will make sense in places like Africa indeed! but i don't see this implemented in other area's.
Maybe when the other point is a registered hub it might work but otherwise would spoil the game too much in my opinion
ABCBA flights are needed even for the big sexy countries. For example, if you have hubs in Lyon, France and Nice, France there is long haul international demand, but it's difficult to serve it completely with 7 day scheduling. However, if A and C can be Lyon and Nice respectively, it makes it much easier to fill up the schedule and flying widebodies becomes economical. This is even more useful/needed now that you can have more bases. France has other good examples of this when you throw in places like Tahiti, St Maarten, and Reunion.
Once upon a time, there were no bases--you picked a single airport and were stuck with it, but you could fly ABCBA routes. This was "abused" by making C the same airport for every flight and players would have a defacto second base at no additional cost. I had epic airline once upon a time based out of Atlanta where every route was ABCBA and the C airport was ORD. Add the fact you could use flying carpets (I had hundreds of Dash-8's in an all C/F config) and you could crush it. Flying carpets are now gone, but the ABCBA routes disappeared after the implementation of bases to prevent players from creating "free" bases. I believe it was also eliminated to prevent players from having over 100 aircraft at non-home bases since your home base is uncapped, but since the rules have since changed I'm not too sure why ABCBA routes wouldn't be added back in with the caveat that C is an existing base. The only way to game the system otherwise is to avoid the increased commonality costs for aircraft at your non-home base.