SEA-GRU is extremely unlikely. Could only happen if SEA grew substantially larger in East Asia. They obviously planning on growing SEA-East Asia, but I don't think it will grow to the point that it would have enough traffic to support onward connections to GRU.

For SEA, I could see 787 making service viable to: TPE, MNL, SIN, BOM, DEL. I could see them trying KIX, KUL, CGK, and BKK, but I don't think those would be successful. If added service to TPE and KIX were successful, and existing service from SEA to HKG, NRT(ideally subbed out with daytime HND), ICN, PEK, PVG all had substantial growth, then SEA-GRU could maybe viable.