The way I understand it is that Fly540 and Fly Kumba is two totally different projects, both planning new airlines in Zim.
Fly540 with ATRs or Dash8s starting domestic flights in Zim, then adding regional flights to Lusaka, Lilongwe, Beira, Lubumbashi...not interested in routes to South Africa.
Fly Kumba with 737-200s (the "next gen" ones...haha) as a low-cost airline starting with HRE-JNB and then domestic and VFA-JNB.
Both have a different model and focus.