Actually its very easy to get high degrees of compliance with minimal cost and effort and if SARS has things properly in place. It boils down to getting services that are charged for abroad to fill out the additional paper work to claim back various taxes from the exporting country and paying over money to SARS.
Microsoft, Google and Apple are already fully on board - it simply makes more sense for them to comply than not to.
At the moment we buy Microsoft download products through Ireland because of its export friendly position within the EU but IFAIK we are actually paying 17% VAT. Now if compliance makes setting up shop in some form here and using a 14% VAT base which serves the region its a big win.
This sort of thing is already done on high value service contracts in legal, financial and management service industries. And in fact VAT arbitrage is something which some firms really do use for tax exporting
What is going to be an issue is if SARS starts to be bullies on little businesses and adopting an attitude of making the purchaser rather than the vendor liable civil and criminally. There is a potential problem in the importing of digital goods and services that when you import goods privately we can quite easily implement thresholds and have a "nothing to declare" issue at our airports with a change of responsibility for VAT moving from the vendor to the person bringing the goods in.
Interestingly SARS and thedti have completely different attitudes towards imports and take a look at the Business Licensing Bill to get a wiff of the protectionist alternatives.