Of course there will be a 730 - the 630 is a budget device -the 630/930 stars another round for the lumia line up and there is a lot of room to fill the gap between the 630 and 930 - I expect Nokia to release the 730 and 830 soon
Let's hope if they do release them they don't degrade them like they did the 600 series. I would be happy with a 830 if they just increase screen to 4.5/4.7, bigger battery, quad core processor, 16 GBP internal men, must keep ad slot and removable battery.