I've never thought about it, but why does the adjective follow the noun it modifies? Is there a technical term for this?
"Someone, anybody, something" are no nouns, but indefinite pronouns. Nouns can be used with an article and normally have a plural. You can't say "the someone" or "someones". "Something new, something interesting" have the correct order of words and such structures can be derived from reduced relative clauses as John Lawler explained in his comment above. So "something new" derives from "something that is new".
Though I know such structures because they are the same in German I never thought about how they evolved. My thanks to John Lawler for helping out.