Then the problem is an academic endeavor and hopefully not something to be sold to a customer. If it is open source, then it is likely to fall into disuse like 99.9% of open source endeavors. If it is in the 0.1% of open source projects then the community will find the effort for a rewrite, but it could be painful like python 2/3 or perl 6/7
I usually iterate. Building upon what was already built.
All to often a 'prototype' becomes the finished product without the intervening iterations. If that was the plan from the start it works more smoothly.
