[desc]

Indeed. I think the key point here is that even if the rewrite 'only' takes 4 years, how many new features have been added to the original codebase (maintained for 'continuity') in the meantime?

There's usually some expectation that the rewrite will make it 'quicker' to develop these new features so of course it will catch up. Eventually. After ten years of splitting the dev team to maintain two codebases. One of which has not produced any value in that time.

Alternatively the application featureset is frozen for the duration of the rewrite, and the company folds halfway through.