Sadly, I don't think any game is going to be a proper alternative to ED in the next 12 months, or even 24 at least.
- X Foundations might make a dent, but it seems too focused on economic empire building, has no planets and no exploration. It does seem to have a more responsive world, where player actions matter more.
- Infinity Battlescape has the looks, but it's only cokbat and only multiplayer. Might make a dent, when released, in the PvP community.
- Star Citizen will never release as a complete, playable game. While it's thoretical premise is, indeed, the ultimate game, every new demo they show makes the game feel even further away from an actual release than the year before.
- Evochon is IMO the only other currently released space sim game even worth mentioning, many rough edges, and production value ir far below ED for obvious reasons (and it show), but It did manage many extremely impressive things for many years now. If it's team had even a fraction of ED's resources, we'd probably be asking if Evochron would still be THE space game in 12 months.
- There are many nice looking space games in development, several on early access, but most are more focused on survival/building than actually being a space sim.
- Starfield will be an RPG. Which is great anyway, I love open world RPG's, so while it won't be an "ED alternative" as in "a space sim", if it's anything like Skyrim or even Oblivion or Fallout but in a scifi setting, I'll have a game to play for the next few years without looking anywhere else (except CDPR's Cyberpunk, I will definitively look at it too).
For better or for worse, ED will still be all there is for the foreseable future in the space sim department. But being fair, it's not simply for the lack of competition, while ED definitively has it's flaws (some quite terrible), is also has plenty of things that are downright incredible, and whenever competition comes, or ED is surpassed by some other game, ED will have had it's name carved out, with due merit, in the history of gaming.