ODD takes huge amount of space and weight.
As iMacs and rMBPs, stopped having them integrated, they will probably disappear.
They will probably be available through USB and Mac Pro models only.
I dont mind about them making it lighter but Im still against the loss of all these parts.
Yes they will be lighter, more compact, etc etc.
But becoming more retina-ized means no upgradable parts.
RAM soldered on to the logic, SSDs cost more since they arent traditional 2.5in, no ODD=no Optibay.
The rMBP can only have 768GB SSD.
But with the old models, you can have 2 SSD/HDDs with optibay.
Space wont be an issue in 10 years or so. But it will be pricey for the next few years.