If Trump were to claim a value for his assets (like Trump Tower) on his tax forms could various governments (the city of New York, the state of New York, etc.) use those to determine the just compensation they would need to pay him if they took those properties under eminent domain? That could result in the government getting a bargain if Trump undervalued those assets on his taxes.
Or could they use information on the tax returns to justify the eminent domain entirely under Kelo v. City of New London? “Trump’s tax returns state he paid $X for taxes on Trump Tower. We have an offer from another private owner to pay $(X+1) in taxes instead.”