Realistically? Egosoft. They have the potential to take Elite and make a really compelling offline game. It would need to be "Elite Dangerous 2.0", because there's a lot of crap in ED that they would need to scrap and / or replace with their own flavor of gameplay.
While I love both Space Engineers and No Man's Sky, I just don't think either of these games would produce good "offspring" if mated with ED. I'm talking specific code rather than concepts (I'd love to have NMS-like procedural flora & fauna and SE-like ship interiors and systems). X4 feels like the closest match, and therefore the most compatible "mate" for Elite.
There are a lot of games that I wished would be more like Elite over the years.
The X-series dissappointed because they are pretend space games, really just connected rooms with sky-boxes. Good games and there is nothing else like them but not space games.
I liked No-Mans-Sky, but then it got all community-event-ridden and lost the whole space explory thing. I have high hopes for it though as they have still kept the survival element quite strong and keep pushing new content.
EvE is also not really a space game but it is a good pvp economy and stat-battle game.
ED has a great space environment but somehow doesn't reproduce the feel of Elite for me. Again - it is a tough one because Elite was single-player and it is easier to create the world you want in your imagination with that.
Martin Schweiger's Orbiter has been the only space-sim I have ever found to produce the feel of being in space in a space craft, and with some mods it even has a bit of a game going for it. ED was never going to go down that realism road but I imagine if it did then that would be my perfect game. Not for everyone though.