There was a time when any Russian military equipment offered to forces on the Korean peninsula would have stopped slightly north of the 38th parallel, but those days are apparently over.
Although only 18 months beyond first flight, the Sukhoi PAK-FA stealth fighter has been offered to the South Koreans for FX-III. Local reports (see here and here) in Seoul today say that South Korea's defence acquisition agency -- DAPA -- has included the PAK-FA in its short-list of competitors.
For those keeping score, this is the first real competition between the PAK-FA and any foreign fighter. South Korea also is considering the Boeing F-15SE Silent Eagle, Eurofighter Typhoon and the Lockheed Martin F-35 Joint Strike Fighter. This could get interesting, folks.