You said that the 5 federal states represent 5 clannist states and your suggestion was to change it to 18 regions. These 18 regions will be represented in the parliament and they will form political alliances... based on clan!I don't understand. If your contention is that these administrative regions will have dominant clan due to demographics, there is nothing that can be done about it (unless you would like to suggest a more radical plan?).
Your original issue was that federalism is more democratic and representative than a centralised political system. I've addressed this in my post. Each of these new regions will be still be representative of the locals but we avoid the problem of consolidated clan states; and a political system that reifies further division.
I suspect as time goes on, and Somalia begins rapid development, these archaic forms of social identification will dissipate as I have discussed here.
I don't see how this will end clannism, at all.