That is the biggest burden in Namibia: 210 is irreplacable and they are all getting old. The Namibian Market is probably too small to justify developments of a new model by the aviation industry. Times have changed were aircraft such as Cirrus are attractive for private aircraft owners - however these are not made to operate in the bush environment at all and do not offer the same payload specs. Speed is important and the 210 offers that, which also makes even the longer flights more bearable for the pax.
It also depends on the type of operation: if you are just doing pickup and drop off roundtrips like Sefofane, you could probably do everything in a Van. Flying Safaris with just 2-4 pax on board would just fall out of the programme or the booking agents would just have to be more organized to sell bigger tours and the sense of being on your own private tour would fall away and operators will also be far less flexible. That is where it also shows, how inovative a country is - in New Zealand you get PAC, Airvan in Australia etc that actually engineer aircraft for their local needs. In Namibia one probably can't expect such "innovation" even though it may be very appropriate - to have a fast, true 6 seater payload, turbine-powered high-wing bushplane.
I know the 206 is not as attractive, but it would be the only aircraft availiable that would come slightly close to offering the same kind of experience for the pax, as a 210 would offer - at a slightly higher cost factor due to lack of speed. But why are there few 206's around in Nam ? (I believe V5-ORX went down and is a write off or is she still flying?). I think it is due to the fact that there are very few operators that would actually buy new aircraft out of the box, at least that I know of and many are living off the second hand investments, that they made 10 or more years ago.
How much weight this poses on the safety issue discussed here, I don't know. As we have seen with V5-ORX - even newer models can be involved in accidents. I think first of all it is the "brain" sitting in the left seat as it is the operator and the maintainance guys servicing the aircraft, responsible for the condition, that should be looked at.