The purpose of it doesn’t really determine whether or not the taxing authority has the authority to levy tax or not. This is all a fight to try to stop taxation of capital until/unless it is sold,at which point capital gains taxes apply. If it’s unconstitutional to tax that equity in a foreign property/enterprise solely because it isn’t income (distribution, dividend, other payment) then I don’t see how it would be constitutional to tax a stake or equity in real estate.
Of course, I’m being slightly facetious here. Obviously we have a long history of taxing property, so I don’t see how logically this tax is unconstitutional either. In the same vein, the US also taxes foreign income that has no real nexus in the US, so if that’s fine I fail to see how they can’t tax a citizen’s foreign assets.