What is the matrix clause of this?

Question

"I accept there's something strange about you, probably nothing a good beating wouldn't have cured –– and as for all this about your parents, well, they were weirdos, no denying it, and the world's better off without them in my opinion - asked for all they got, getting mixed up with these wizarding types - just what I expected, always knew they'd come to a sticky end ––"
(Harry Potter and the Sorcerer's Stone)

I suppose the construction might be a preterite perfect. In this case, I wonder what the full matrix clause is supposed to be. I guess it could be ‘There would have probably been nothing [a good beating wouldn’t have cured]’. But I’m not sure for I’ve already got one:” "Your strangeness is nothing [pronoun functioning as subject complement] that (relative pronoun) a good beating wouldn't have cured," which makes me confused. What could be the matrix clause?

Answer 1

The clause in question stands in apposition to the NP which is the complement of 's in the previous clause, so it shares its precedent's syntactic role; nothing parallels something:

I accept that
there’s
    something strange about you
it’s
probably nothing [which] a good beating wouldn't have cured

ADDED:
The double negative in nothing which a good beating wouldn’t have cured is perhaps confusing. Dursley regards Harry’s strangeness as a character flaw which a good beating would have cured if it had been administered early enough. In this clause Dursley rejects the alternative interpretation, that Harry’s strangeness is something innate which a good beating would not have cured. Nothing here should be understood as not something:

It is not something which a good beating would not have cured.