Roads won't be maintained and are hard to monetise. A railway would probably be more economical, profitable and safer since no one hijacks trains anymore since the days of the wild west.
A train would be the ideal, but a simple 2 lane highway would transform the region, and put Kismayo in direct competition with Djibouti for the business of southern Ethiopia. The Ethiopians have already constructed a tarmac road linking Addis to Dolo Ado on the other side.of the border. It would open up a huge part of Ethiopia, and would probably be very competitive with Djibouti and Berber in terms of Chinese imports into Ethiopia and East Africa in general. Something resembling the urbanization between Djibouti port and Dir Dhabe would probably also happen. It would also make it easier to move agricultural goods out of the Juba valley. Three birds with one stone.
A Kismayo-Dolo road would change southern Somalia's economy almost totally.