According to nearby boroughs heads - flooding of the area should start before the end of 2015 (optimistic version), and it may take 2 years to complete the filling. Next thing is proper infrastructure development - but the boroughs doesn't have enough money for it yet. So concluding - it's hard to say more specific when the whole investment will be complete. It's Poland. Usually everything takes more time than predicted.
But does anyone know if it will be possible to buy land nearby?
It depends from landscaping policy for this area, ask local authorities.