Not a space sim, but you might want to check out Vector Thrust. It's inspired by Ace Combat but has a lot of improvements/changes to make it feel a bit different. I'd say it has superior mechanics with cool stuff like post-stall manoeuvring(a bit exaggerated for coolness) and gravity affecting missiles.
It has a more robust electronic warfare system based on a lot of factors like enemy jammers, friendly AWACS, your own aircraft's electronics and stealth ratings, etc. Things like radar jamming, phantom targets, reduced/improved missile guidance, and stealth. Some of these things could be translated into a space environment.
The campaign is rather ~meh and it lacks a tutorial, things that definitely detract from the game but it's an indie title so great stories and voice acting aren't something most people expect. Also, I don't remember anyone ever calling their missiles, so you don't get that Ace Combat-ey "fox 2!, fox 2!".
It's also pretty mod friendly, though like 90% of the skins are either Ace Combat skins or cute anime grills from idol shows(mostly Idolm@ster, Love Live, and Utahime).
It's 50% off on Steam right now so you might want to check it out. Not space, but might be worth seeing what other indie arcade flight sims are doing right now.