In terms of grammar, "This being x," is an absolute clause.
Being is a particple and is not a half-gerund (a gerund with an accusative instead of a possesive, e.g. "me eating loudly irks Bob", which is considered ungrammatical/illiterate by prescriptivists). It is not a dangling participle as being refers to "this".
The whole clause does not depend on the main clause nor is obviously the main clause dependant on it, therefore it is said to be absolute. It basically is an adverbial clause that is not dependent. It is considered a grammatically correct construct, albeit a rarely used one.
The "This being x" construct appears relatively frequently in Stephen Fry's books. The best place to spot absolute clauses is in the writing of many Greek authors in English (J. Eugenedes excluded) as participles play a bit part in Greek.