I'm no linguist and I'm unaware of the recent development in linguistics, let alone all the past developments, but I know some of the past developments at the very least, so I'm asking this question to anyone who is well versed in the current linguistic development. (So if you're not familiar with the recent development, please don't bother to downvote this post or answer my question simply because it doesn't make sense to your traditional linguistic knowledge. Not that I really care about this post being downvoted or even being cluttered with boring answers, but that I'd really like to know if there's anyone out there who can think outside the box without getting carried away with the box itself.)
As far as I know, there is a well-known distinction between a grammatical subject and a logical subject. The former concerns syntax, the latter semantics. The two subjects sometimes are the same as in:
I have no idea.
Here, both the subjects are "I" and no other.
But sometimes, depending on whether we want the former or the latter, we might get a different subject in the same sentence. Please see the following dialogue between A and B:
A: There is chaos.
B: That I know.
In A's line, the grammatical subject is "There", as shown in a counterpart interrogative "Is there chaos?" (the subject-auxiliary inversion), whereas the logical subject is "chaos" because A is not talking about "there" but "chaos".
Now moving on to B's line, both the grammatical and logical subject are "I" under the traditional definition of these terms. And they say that "That" is the object of the verb "know" and it is simply placed in front of the subject "I". Right? (If this is not what is normally accepted, please let me know.)
Is there any new development in linguistics that considers "That" in B's line the subject, be it the grammatical subject or the logical subject or some new kind of subject? Because, syntactically, "That" occupies the position of the subject, and semantically "That" is essentially what B is talking about.
Oxford Dictionaries Online has this definition for "subject":
Grammar A noun or noun phrase functioning as one of the main components of a clause, being the element about which the rest of the clause is predicated.
Applying this definition to B's sentence, "That" can be considered "a noun functioning one of the main components of a clause", and the rest of the clause "I know" predicated about "That".