The issue is that every driver implementation ever ships with a slightly different implementation of that complex parser. That means (every mobile device)X(ever

The issue is that every driver implementation ever ships with a slightly different implementation of that complex parser. That means (every mobile device)X(every OS update) and (every PC ad-in card)X(every driver update) all have the potential to misinterpret/reject your shaders in slightly different ways. This doesn't have anything to do with shaders as strings. It's been true since the beginning of shader programming, whether bytecode shaders or otherwise.