SVO is the main SU hub is it not? Surely of all the Moscow airports that is the best one for SU to serve from LGW as it allows the bulk of thier network to be accessed for those not just going to Moscow.
A low cost carrier to Russia would be good, but I feel it is better for S7 to take the mantle from Transaero as at least they can offer connections either end, through oneworld. easyJet were a good choice on paper, but is it the right product for Russia? It is a route which even BA, in their race to match easyJet, still offer an enhanced in flight product on and treat it as a full service "medium haul" flight. What other carrier could take the route over from the UK end I don't know.