Diving into the unknowable: a misguided experiment
I find the idea that tikanga is a form of law very puzzling. H. L. A Hart, for instance, argued that law comes into existence only when the "primary rules of obligation" that all societies have are combined with secondary rules that enable the primary rules to be spelled out clearly, deliberately altered, and systematically applied. Something like this seems to be essential to any concept of law, but tikanga does not have these features. How can these presumably learned judges be forgetting this?
Yes, you are correct. A natural reaction to take advantage of a potential revenue stream, especially if you are looking for work from government bureaucracies.
By 1840 many Māori leaders had realized that times had changed and that tikanga could not prevent the devastation of what we now call the "musket wars". The rule of law, with which many were familiar from visits to Sydney, seemed preferable. That's why they signed the Treaty. This was the law (te ture) to which the first Māori King encouraged his followers to hold fast (kia mau), even when the governor violated it. I have enormous respect for the wisdom of those Māori leaders.
I note that already some of the large law firms are promoting their tikanga capabilities. It is a potential gravy train for lawyers. These judges are blowing the whistle so it can leave the station.