I mean English has such a bizarro spelling system it may as well use pictograms. You might as well say "English will never be a lingua franca unless the English speakers overhaul their spelling". English is where it is because of the double historical whammy of the British Empire followed by American hegemony. Couple battles won or lost here and there and we'd still be using French.

Just as the saying is that a dialect is a "language with an army and a navy", a lingua franca is a language with the biggest army and navy (or trade/cultural influence). It has nothing, absolutely nothing, to do with the simplicity of the language, although simplified pidgins/creoles might develop as more non-natives have to learn it (hence how Latin evolved into French, Spanish etc). But pidgins/creoles tend to be localised adaptations and don't have the universal currency of a lingua franca - unless of course they develop into fully-fledged "imperial" languages themselves, as with English.