It generally takes 2-3 years for a weight-class to really develop and become marketable, and sometimes it just doesn't work at all.. (flyweight is basically collapsing and a ton of talent was thrown at it)
The fear of 125 is that many women at 135 would drop down, and then no one would fight Ronda (this was before she lost). If Tate hadn't had new boobs and if Holm hadn't beaten Ronda than this statement would still be accurate. Also both women's divisions are still fairly slim in talent and 115 is just getting its legs..
145 could work, but again, the development process is slow, and they would need a solid 10-15 women to start off with, but I could see Cyborg leading that division to some good ppv feedback the same way Ronda carried 135.