I do believe that Sabunta would soon disappear or merge with Jumia.com.ng since it doesn't make sense for them to be competing with one another in the same market.
Changing it from a dot com to a dot com dot ng. also presumes that Jumia would be more favorable as an African brand instead of Kasuwa or Sabunta which were derived from Nigerian languages. Check out the other Jumia sites - Jumia Egypt, Jumia Morocco. (This is akin to Dealfish rebranding to OLX)
This new name may also not be unconnected with the recent joint agreement between Rocket Internet and Millicom International Cellular to jointly develop franchises in the online sector in Latin America and Africa
As least, it was expected that Rocket Internet would exit the market as soon it got a juicy offer. Guess Millicom is the answer.
P.S Don't ask me what Jumia is. I don't know
Update: Kasuwa and Sabunta have merged into one entity - Jumia