I'm not convinced of any counter arguments as of yet. I never tried to make an all-noun language, but now that I look at it, I simply don't see anything more to it. 

Of course it can be a matter of definition - what is a part of speech? Wikipedia says: "Commonly listed English parts of speech are noun, verb, adjective, adverb, pronoun, preposition, conjunction, interjection, and sometimes numeral, article or determiner."

The fundamental language can express all these, but using nouns only to express them. It is not so unusual, e.g. 'million' is grammatically a noun in English, not a numeral. Similarly 'inside' can be a noun in English; instead of writing [in house] in FL you can write [inside house] which reads semantically "in the inside of house". 

The parse tree is a 2D language - I don't think it was mentioned it mustn't be one. But parse trees are much, much older than generators; they don't have to be generated by machine. You can draw them or just think about them. Like I said in the introduction post, I prefer a mind map. 

However I did also propose ways to speak FL. For example, I have the sentence "Boy nominative action, hill top accusative action, house accusative action, see action." (This is the regular grammar S -> | aS; as I mentioned earlier, 'top' can be used instead of 'on', and 'action' can be used instead of 'topic'.)

Shouldn't this be pretty straight forward: just show me which of these words are not nouns!

Suppose you'll agree at this point that it's all nouns, but someone goes on to argue that it's not unambiguous (whether that was required or not) . That's a mistake because now that we have the sentence, _now_ we'll have to think of how to generate the correct parse tree for it, and we already know exactly what it must look like. The correct parse tree is this: [action [nominative boy] [accusative [top hill] house] see]. If this tree is ambiguous, then there is no unambiguous!