Off the top of my head:
Advantages: can use one modern engine, whether Su27 or MiG29 (probably Flanker). So less maintenance that way. Also gets more engines of that type built in general, which makes greater economies of scale (see the US using F100 on both F15 and F16, and F110s on both F14 and F16). So that engine is cheaper and the Russians have more spare parts in general.
Disadvantages: old airframes. Anything swing-wing takes a lot of maintenance, so that's got to go. But that also messes with your STOL performance. So we're probably talking about needing a supersonic supercritical wing with leading edge slats and triple-slotted flaps, basically a miniature Boeing wing with a bit more sweep to it. Maybe even blown flaps. All of which increases maintenance, but not as much as swing-wing.