I disagree. I think that Skrall should have been replaced by a visorak. There aren’t any notable/iconic green dark hunters who could replace Gresh. Also from a non-story perspective, it would be strange seeing an enemy of the toa fighting alongside them. Plus, Gresh represents 2009.
EDIT
I imagine that the Visorak (Oohnorak) would look something like this:
A modified Agori build frame
Then, there would be a new rubber black and white (or maybe black and lime green?) melded carapace piece. The rubber piece would cover the open ball joint at the back.
This way, the Visorak would fit into the scale of the stars, while also providing a unique (compared to the rest of the stars) and good looking (in my opinion) set. And it would represent 2005.