In the sentence "it is natural that manufacturers' capital avoided Brund", the that-clause functions as the subject.
Yes, Michael, this is one interpretation. In fact, it might be the more prevalent interpretation.
In a linguistics class at Georgetown University -- quite a while ago -- I wrote an assigned paper on noun clauses and their syntactic function in the sentence. I note that I identified constructions like this one in this manner: 'As adjective complement (or delayed subject).' This was a topic that the professor discussed and interpreted in both ways.
Some sentences in the paper are It is clear that the suspect is innocent
and It is good that Jack is not coming.
I got an A on the paper from Professor Ross McDonald, so I'm assuming that I interpreted correctly, at least according to him.
Now, thinking about describing these sentences, I still believe they can go either way. I see that many current texts, Swan* being one, treat this construction as a delayed subject.
Others, like Focus on Grammar** treat the construction as an adjective complement, with examples like these: It is important (that) people develop a sense of humor
and It's clear that laughter involves an emotion
So, Michael, do you think we can describe this noun clause in two ways?
*Practical English Usage, third edition, by Michael Swan. Oxford 2005
**Focus on Grammar 5, third edition, by Jay Maurer. Pearson Longman 2006