AC3 plot can be considered non-canon (everything that happened within the simulations), but the base story is canon for sure and the possibility of having any outcome from the simulation becoming a reality is very likely...unless the simulations themselves opens another path. The actual happenings.
Now, while Neucom and General Resource took over the world (or at least Usea), I could imagine governments still functioning and existing. Just that they're not as capable of shifting the world economy as they were able before. (Hence, the existence of UPEO, the armed forces from the Neo United Nations). So if the NUN exists, then there must be nations to begin with.
So, taking this into account, I can imagine the Kingdom of Erusea (previously known as Federal Republic of Erusea) as an existing nation, provided that it doesn't get wiped out in AC7.
If Erusea still existed, we could affirm they would continue to operate Flankers from 2020 and beyond. So I reimagined the AC04 non-SP Erusea skin for the Su-37 and put it into an airframe resembling the Su-35. In my case I simply took the Su-37 airframe from AC3 game files available thanks to Krishty Model Viewer and removed the canards in Photoshop.
Now, why would Erusea pick up COFFIN tech?
There are some benefits of using it. First of them, you can make the whole surface with RAM (radar-absorbent material). You can reinforce the cockpit, get a 360 view outside the aircraft (and replace the info provided with IR imagery for improved sight in certain scenario, or overlay the view with data), and finally, you can use a common interface among many aircraft.
Next up, F-15S/MT+ in Emmeria colors (or might modify the S/MT+ to make it look like a normal F-15).