I've looked into some of it further.
On the scheduling. I'm disappointed Plunket Shield is reduced to 8 rounds, but NZC this year have an NZ A tour away to UAE to play Pakistan and also have an incoming tour by India A. That is 5 extra FC games (plus plenty of whiteball games) for the fringe players.
I'm not sure if one is a financial trade-off for the other.
NZC contract the domestic player for 7 months. Whether they play 8 rounds or 10 rounds is fairly irrelevant, although there would be operational costs in hosting those 6 matches.
I've looked at the rest of the domestic calendar. There are the same number of rounds of List A and T20, so no other comp has expanded at the expense of the other. So it can only be a financial rather than playing reason.
On the financial side. The annual report is due out in a few weeks so probably not worth getting stuck into that yet. Looking at last years report they made a $10m loss and explained they have a squeeze for a few years until 2023
White said NZC faced a "challenging couple of years" but explained the loss was largely due to the International Cricket Council's new financial model. In the eight years till 2023, NZC's slice of ICC funding would increase from US$90m to US$128m but it was a case of less now, more later.
https://www.stuff.co.nz/sport/cricket/98666541/nz-cricket-to-declare-93-million-loss-as-it-locks-in-big-indian-broadcast-deal
I hope that a reduced Plunket Shield doesn't get institutionalised before the money starts coming back in.