Even if you induce neuronal growth, the brain will have to relearn the connections it needs to make, which took a lifetime to form. Forget about playing the piano again. You'll have to relearn to play (although you'll still have the conceptual knowledge).
Wrong. The striatum (which governs procedural memory) is only indirectly affected in parkinson's. Parkinson's is caused by the death of dopamine producing cells in the substantia nigra which is the region that communicates with the striatum. The memory of these movements (such as playing a piano) is still there, but the ability to access them is not. One of the things that is noticeable about parkinson's patients is that many of the jerky movements and tics caused by the medication are often movements that would otherwise be normal in a different setting (some of the ones I've seen include: moving pieces on a chess board, dancing and writing on a blackboard).
Getting stuff to grow is easy, just kill of the p70 gene. Getting stuff to grow safely is hard. Very very hard. Loads of research still need to be done before this can really be risked in a live human being.
would you care to give a reference for p70 being used to create iPS (induced pluripotency)? As far as I am aware the genes typically used are oct-4, sox2, c-myc, nanog, lin28, klf4 and p53 (both p53 and c-myc are oncogenes, the rest are not) Interestingly a paper was published a few months ago which describes a method for transient expression of these genes. This eliminates (or at least greatly reduces) the risk of cancer arising from stem cell treatment as the expression of any oncogenes is only long enough to revert the cell back to a pluripotent state.
When Dexter's on the Internet, can Hell be far behind?"