I like the list by Askavir, but would modify it thus:
1 - Scanning mechanics that require player skill (and is improved by player cooperation either in wings or as crew serving a "Scanner" role). Actual gameplay and skill required to find USS, planetary POIs, ships not in supercruise, especially rich sites for ore and materials, etc. To enrich the gameplay experience for explorers, asteroid miners, surface miners, mission runners, pirates and bounty hunters... This ties together with nr 2:
2 - USS revamp. Ditch the random spawns. Allow people to investigate the USSs they find nteresting, instead of waiting for random stuff. Use detailed surface scanner to locate ground POIs and material rich regions. Ditch the whole peek-a-boo POIs mechanic (and lets no speak of them again - ever).
3 - Better networking and instancing. This would really help the social aspect of the game.
4 - Better crime and punishment system. To encourage more people to play in OPEN - to share and enrich the experience for everyone.
5 - Powerplay merge with BGS, instead of being a game within itself (like so many other things in ED). Have players contribute to powerplay factions by doing "regular" BGS tasks. Have minor factions have powerplay allegiances instead of superpower allegiances. Make your powerplay faction reputation stack on top of the minor faction reputation to allow access to better mission rewards. Tie naval ranks/careers to powerplay.
6 - More planetary content. Air to ground base attack, using ships (not dune buggies) to destroy ground installations protected by AAA sites, missile launchers and other ships. Ground facilities only accessible though the SRV, without landing pads but with "parking pads" which provide services, missions, etc.
7 - Wings reward sharing. All profits made by any of the wing members in a wing should be split evenly between all wing members, be it either bounties, combat bonds, mission rewards, trade profits, etc etc.
8 - Make those formidable CQC assets in game serve a purpose. Make them dockable, and provide missions.
9 - More passenger content. Troop deployement, emergency evacs, prisoner transport, etc.
10 - Atmospheric planets. And please note: I am longing to see atmospheric planets! I almost can´t wait. But they are here at the bottom of my list because the above is probably less taxing on development time, and honestly, the game needs to fix and improve some of the basic mechanics. (Did I mention scanning gameplay?)