I highly doubt they will do this but here would be my suggestions; and to add to credibility...I design develop systems for a living.

Upgrade the Engine
It is quite obvious that many of XIV's technical limitations are due to the game originally being developed for the PC and PS3. The lighting, shadows, and even character meshes, models, and normal mappings are all subpar compared to modern AAA games. Heck, this game looks worse than TERA and BnS and too close to FFXI.

We're in 2018. Look at Black Desert Online, Blade and Soul, and TERA. If we get into the single player realm, Monster Hunter World, Witcher 3, and many others are rivaling BDO. Graphics, physics, lighting, shadows, and all of this matters because video games have become more and more immersive. When someone goes from, say, Monster Hunter World to XIV, the very first thing they're gonna notice is "why is everything so flat and bland?"

Move to Real Time Combat
Tab targeting is antiquated. The reason tab targeting existed in the first place was due to technical limitations in the old days. WoW has slowly been moving away from tab targeting with many skills becoming free aiming. Tab targeting, believe it or not, needs to go similar to turn based combat which was also done due to technical limitations (and why everything now is real time). While I do not mind it tab targeting, many of my friends who have tried to get into XIV have described it as "too slow and boring."

Streamline the MSQ for ARR
As others have state, this takes too long to run through, and has way too much filler content. Revamp it. I tried to get my fiancee into XIV and she straight up told me it was too boring. We're now playing Elder Scrolls Online together instead.

NOTE
I mentioned BDO, BnS, and TERA a lot. The reason why I am not playing any of those games is because Square-Enix is a FAR MORE reputable company that have built a reputation from accepting their mistake (FFXIV 1.0), and literally pulling off a miracle with ARR. As a software developer and long time gamer, they've gained immense respect from me by doing this as I've been involved in projects that have sank due to disregarding customer feedback, and seen games do the same (Hellgate London anyone?) So please do not take the above as bashing...I'm simply stating obvious trends. And while I don't mind XIV's tab targeting....the fact that I can't get anyone to play with me is a pretty good indicator as to what's wrong.