> Now the complicated part is how to define a company. We don't want a single company to just split itself into 2 legal entities

HN routinely seems unaware that this is a totally solved problem in the tax law of virtually every industrialized country.

In the US, for example, the phrase is "Common Control": https://www.law.cornell.edu/cfr/text/26/1.414(c)-2

All sorts of modern tax schemes would have truck-sized loopholes without a rigorous definition of Common Control. It's already in the tax code of every industrialized country (possibly under a different name). All you have to do is reference it. The necessary definitions have been in the tax codes since the 1980s.

I'm kind of annoyed at how often this "but but but two companies with overlapping owners yadda yadda" comes up. Go ahead try that on the IRS and see how it works out for you.