I really, really, really hope this includes some balance work, too. I love(d) this game to death and sank countless hours into it, but ultimately just got so frustrated and disappointed with the balance issues that I had to leave. I just couldn't enjoy the game anymore when the foundation was so severely screwed up.
Defensive modules (SCBs, hull reinforcement, etc.) eealy need to not be allowed in standard internal slots. As long as defensive modules are competing for space with all of the other modules needed to interact with the game's content, there will always be a monumental divide between the players going about their business generally trying to engage with / immerse themselves in the world, and players that are only interested in fighting / killing other ships. Making defensive modules military-slot-only, and making sure all ships have at least a few military slots to compensate, would make an enormous difference on unifying the playerbase (at least when it comes to builds, and ship capabilities). It would also help immensely in the challenge of trying to balance player power levels vs. NPCs by narrowing the range of possible survivability levels of player ships.
Engineering is a mess, too, but I'm not sure of how practical it would be to fix at this point. It has always needed to be more about customization, specialization, and side-grading, rather than the absolutely ENORMOUS raw power increase it offers now. Your choice to grandfather old weapons with the big engineering rework however makes me think it's very unlikely you have any desire to ever rectify this issue though, so I'm not holding my breath.
And finally, the systematic demphasis and practical removal of the "blue zone" system with flight is probably the saddest development. The fundamental choice of getting either maximum speed OR maximum maneuverablity, but never both, was the thing that really set Elite: Dangerous' flight system apart. It's what really made me fall in love with the game- the way it felt to fly. Boosting has always allowed you to temporarily ignore that system, but it used to be something you could only do occasionally, and at significant cost. Between engineering, and ships getting released with more and more boosting ability even with factory-spec A-rated stuff (yet more and more floatiness) has changed this, though. Boosting constantly is the norm, which means ignoring the blue zone constantly is the norm. Instead of needing to carefully manage your velocity and engine power, it's all about ping-ponging around, twitch aim with FA-off, and slapping away at massive health pools. I see people refer to actually needing to deal with the blue zone mechanic in the brief moments where they're not boosting refer to it as "stalling". It makes me sad. The soul is gone. All the other balance issues undermine the game heavily, but killing the soul of the flying itself is the thing that ultimately drove the final nail in the coffin of my fun in the game.