It seems they finally discovered small 40-50 seater jets do not have the range required (including a possible deviation to ASI).
The focus is now on larger aircraft, as Baroness Verma declared in the Houase of Lords on 20 June:
We are seeking to establish commercial air services using the southern approach to the runway where wind shear is not a significant issue. A number of aircraft types have been identified which should offer reasonable performance using a southern approach (the Airbus A318 and A319, Boeing 737-600 and 737-700). We are in discussions with airlines on how we can bring one of these into service.
Not so many in service in Southern Africa. Shortlisting aircraft types is one thing, finding an airline in the region that can and wants to operate regular scheduled flights at short notice might be the real challenge.