This UK Guardian story is all messed up unless things have changed drastically in the past few months.
The obvious problem is that although Mark Millar does indeed work for Marvel, where he is responsible for the Ultimate series of books, Marvel doesn’t own Batman or Superman. Marvel and DC are planning a JLA/Avengers crossover book, but there’s been no mention of Millar’s involvement that I’ve heard of.
On the other hand, a Soviet Superman would be a great idea, though DC has already went through several reinventions of its characters. Didn’t the Guardian reporter read Kingdom Come?