Perhaps so. Though I found structural things with each of those projects that I did not like. For example, opentaxsolver's logic is a bunch of 'monolithic' C code, and I haven't been able to find any tests. UStaxes is better in that respect, but there I couldn't get past typescript, honestly, and they have code like https://github.com/ustaxes/UsTaxes/blob/master/src/forms/Y20... where they're relying on position of an item in the array to indicate which field it is. Not trying to disparage anyone, but I did not see evidence of an attention to detail I felt I could trust (and maybe that's just me and NIH syndrome).

What I would really like is to somehow extract out a representation of the tax logic into something separate from the business of collecting the data from the user, or even calculating the results. I'm not entirely sure what that would look like, maybe it would have to be some domain-specific language (eww) in order to be able to fully express the relationships and dependencies between different fields/forms.

But I think that tax logic portion is the difficult-to-maintain part, and also the portion different projects would benefit the most from sharing.