It was already established that he wanted to kill anyone who would pose a threat to his plans but how different would things be if he succeeded in taking over? How would he treat the matoran and agori?
Personally, I think you would have wound up with a somewhat fascistic society. Not a Makuta-sort, where people are just being wantonly killed on a whim. But a very ordered society where Velika’s word is law and there are consequences for not going along with that. I think Velika would have seen himself as a firm father figure and the Matoran and Agori as children who can’t be trusted to make their own decisions. His idea of the GBs taking a firmer hand is just that, they know best and everyone should just do what they say.