Look up the Māori King movement, it's the same idea.
Regardless, I think as much hate as ACT gets for this - it seems obvious that clarity on the principles of the Treaty of Waitangi is required so that every New Zealander knows where they stand (legally speaking) and we can move on as a country.
What does this even mean? You can't just 'move on as a country' if one side tries to unilaterally rewrite their obligations to an agreement. That is what ACT is trying to do, the so-called party of property rights.