The jury is still out, but it seems clear that KSHV is at best simply a co-factor in producing KS, along with the HIV itself and one's suppressed immune system. Prior to the arrival of protease inhibitors, a diagnosis of PML was untreatable and essentially an irreversible death sentence. In light of this, these limited reports of brain lesions shrinking and of improved cognitive function are to be celebrated. This was not universally true, however. It is significant as well that all patients were receiving a protease inhibitor-containing drug regimen, which in itself could account for improvements.
Improved prophylaxis is certainly responsible as well.