Feels to me like a lot of travel at the back end. Namibia to Maun to Vic Falls will add a lot of travel time in the last 3-4 days which will add cost and not let you do too much. I don't know if day trips from Maun are feasible and one night in the Delta isn't enough.

I would think about just focussing on Namibia for the extra time and then back to Jo'burg or Cape Towna at the end. I haven't been to Namibia, but it is on my list and I think there would more than enough to fill in the extra few days.