I suspect it's a matter of time. However, from what I've read most of the soil in Siberia is very poor for farming, so I guess there won't be much food production coming from there even if the climate becomes warmer...
If you really want to, soil quality can be fixed with heavy machinery and chemical fertilizers. But the new, warmer climate isn't particularly stable yet, so it's probably not wise to pour too much resources into that mega-project at this time.