"The goal of the project is to make text hard to read for computers yet fairly easy to read for humans" At first look it doesn't pass the search engine test. https://duckduckgo.com/?q=I%27ve+bien+aloune+whyth+jou+eensi...
What if you want to use it in the opposite direction? Let's call it the CIA/NSA direction, where you know what unobfuscated phrase you want to find, but not how someone may have obfuscated it. This is arguably much harder, especially if you do not store some sort of representation of the content "as sounds/phonemes".