Not true, they have siad numerous times that with the way current game has been written it's almost impossible to improve on some stuff without serious reworkings which would take more work than just doing 2.0.

Also, they did not really do many improvements of the type you are talking about here. Optimization has not been improved, (what issues with gfx engine? really? XIV is one of the worst optimized MMOs ever) UI lag has been only slightly relieved, they can't do anything about retainer lag, problem with objects loading and so on and so on. All improvements are basically contents-side, with changes to battle and classes (yes, still nothing engine wise).