The large factor is the amount of work to create everything again. Plenty has been written about large re-writes, they can and have worked out in the long run,

The large factor is the amount of work to create everything again. Plenty has been written about large re-writes, they can and have worked out in the long run, but generally it takes a decade for the new to be as good as the old - either it is missing critical features or it has too many bugs.