My suggestions:
- Improve class/job quests, have them teach you about the moves and how they work, and get you to understand combos, and stuff like that. Place more value in the quests. Have the class/job duties make you use your combos and cooldowns to progress
- Remove the filler BS from MSQ (2.x and to a lesser extent 3.x)
- Make the new jobs accessible from level 30, so long as you have Stormblood
- Nicking someone else's suggestion here, but this could work really well, is somehow create a tie-off point whereby you don't indulge in the DragonSong War, and instead jump to post-DSW. Where from though, I don't know.

I have friends I'm trying to get into the game. I'm possibly going to wait until all crafters bar CUL are 50 though, so that I can craft them all the stuff they need.