It might be worth a refresh on the DO technology by reading EF Lens Work Book section 9. Download from Canon site somewhere. The benefit claimed of DO elements are they can offer superior colour correction than UD or even Flourite elements. That in turn allows you to make shorter telephoto lenses.
In a wide angle, maybe they don't need to reduce the size, but from what I've seen the 14 II does suffer from some lateral CA so perhaps that can be improved on using DO. Having said that, it is one of the easier things to fix in post processing so wouldn't be high up on my list of things to do.
As for a possible 70-300 DO II, I would love to revisit that. I used to have the 70-300DO although I sacrificed mine towards the L. I do miss the DO in size terms. What it lacked was quality wide open, thus needing to stop down which was somewhat limiting. If they can produce a revised version with better wide open performance at a similar physical size, I'd reconsider it for sure.