Actually frames are able to cast on themselves, cure's being the most obvious, but also WHM can cast Regen IV on itself and BLM cast's dread spikes (the latter is less important as it doesn't cast on player originally).
But I agree that the attachments don't function as pro/shell as I mentioned in my post. Would be nice to increase frames elemental load, with job-points for example.
Also the content of Camets post while awesome, is slightly concerning, the frames I can see most benefiting from Pro/Shell are the RNG/PLD frame, which have no casting abilities. Unless a player would be able to cast Pro/Shell on them, which would be much more useful.