Short answer: It will never happen.
Less short answer: Even with all of your higher level skills being individually synced and scaled down the dungeons aren't designed to accommodate end game skills so cheesing mechanics would be common. Not to mention those additional skills would cause a very noticeable increase in DPS just by being there. More oGCDs to use is always going to result in more DPS than what a level 15 player has access to for example. This dev team has frequently noted that they are very small and even small QOL improvements that were on the agenda get missed from patch cycles occasionally, removing skill sync loss would be a major redesign they simply would not be able to accomplish in the foreseeable future.