I think the idea of moving the wreck of Costa Concordia to upright position on a newly erected sub-sea platform before floating is not the best solution. It is time-consuming and materials-consuming and it is by far more expensive. And definitely it will be impossible to keep it upright during the towing phase.
It would have been better to float and tow it in its tilted position because keeping a damaged ship upright after shifting and distorting its center of gravity and after its bottom cavity was destroyed is clearly huge task.
I suggest a much easier and cheaper approach, as follows:
1. Make many small light weight tanks
2. Sink equal numbers of these tanks on both sides along the length of the wreck
3. Tie each tank with at least three tanks on the opposite side of the wreck with steel cables passing underneath the wreck
4. Tighten the mesh of steel cables to bring the opposite tanks as close as possible
5. Start pumping the water out of the air-tight tanks simultaneously to make them float and lift the wreck
6. Add more connected tanks as much as needed on both sides of the wreck to raise the load substantially
7. While it is afloat and still on its tilted position it is possible to tow the wreck away to a ship dismantling yard
The current operation i as follows: