Having actually worked with James Cooke Brown on Loglan (I wrote the first Yacc grammar for it), I have to say my recollection is that Jim's view was more tenta

Having actually worked with James Cooke Brown on Loglan (I wrote the first Yacc grammar for it), I have to say my recollection is that Jim's view was more tentative and nuanced than you've made it sound. While we certainly enjoyed finding things that seemed easier to say in Loglan than English, I don't recall him ever suggesting that there might be a thought that a non-Loglan speaker couldn't think. I think it would be fairer to say that he was convinced that Whorfian effects were strong enough that there would be value in engineering a language to take advantage of them. But while value is somewhat in the eye of the beholder, I would say this hypothesis has not held up well either.