as a johnny come lately in the ESKOM main thread i thought this might be slightly different - albeit not new…hence this posting; especially after taking note of the frankfort conundrum.
here is the hypothetical situation:
as the middle and lower income groups seem to prefer UPS systems for inter alia cost/migration/ownership issues it does happen that during eskom up-time [eut] [which also becomes more scarce] millions of watts are drawn into batteries to be used during eskom down time [edt]. this energy is then used during said edt. the more people doing this, with concomitant energy loss in the ups systems, the less effective eut, i.e. the less effective the whole loadshedding concept becomes. it might be as yet only a drop in the ocean, especially as industry mostly use solar or gens as backup; nevertheless.
although my dear wife initiated this train of thought i take full responsibility for airing it here 
edit:
afterthought… as soon as a critical point regarding this issue is reached, batteries/inverters used in purely UPS setups might face being taxed or alternatively if those units are used in solar setups they could be subsidized 
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The load saved during loadshedding will likely be somewhat larger than the increased uptime recharge, as most, especially lower economic class systems are unlikely to be powering ovens, geysers, etc. The recharge will be to compensate the one lamp and grandma’s TV. ?
unless they are charging from the grid in an unmetered way they are already “taxed”. You are paying for the inefficiency in the inverting and the recharging in terms of increased kWh used to keep the same 60W light on from the UPS vs straight from the grid.
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On this topic, there will always be a critical point for various subsystems. Water and sewage is one that starts to suffer immediately once you have more than 12 hours downtime. Around 14 to 18 hours, food starts to go bad in freezers and refrigerators, and of course the geyser is also on just about permanently when you get to this point. I think the official term is “diversity”. You lose that diversity, that randomness where not everyone is running the same things at the same time.
Since we no longer refine fuel in South Africa (except for a few barrels at PetroSA), I wonder to what extent transport will be affected. The energy needed to refine a liter of petrol is (apparently, with some fudging because some of the heat is derived by burning lower products) equivalent to 1kWh of electricity, although the oil industry itself claims as low as 0.2kWh/liter. If we still refined our own fuel, we would much sooner reach a point where transport is affected as shortages in fuel develop. I think that is still going to happen, but it is unclear at what point. At least you can burn your own product to dispense it at least.
If we can keep it to stage 8 this winter (and that is a bit if), that would be good. That’s about the worst we can weather.