And generalize it so the underlying framework can be used in other areas, such as manufacturing, where you need to estimate the time/cost to build an assembly, which is itself composed of other subassemblies. Then have the ability to store those subtrees separately, so if you're estimating a new product with some subassemblies you previously estimated, you can reuse that data.

That's a product you can actually sell to any number of small manufacturing businesses worldwide.