Warning: the post has been considered a "tl;dr" by the poster. Summary: reverting to 4.85 won't help; people's interest burns out and they want something fresh; a radical change which would require a server wipe and can either reignite Discovery or finish it off; thanks for everything, Disco, and all the best to you!
Might I remind you that the player activity started dwindling by the end of 4.85 era (that may've happened earlier, but I only joined during the second half of 4.85). And quite a few people were tired of it and were waiting for 4.86 to come out. 4.85 may have been one of the most successful versions, but it still doesn't mean that reverting would change much.
I have good memories about 4.85, but it's mostly because it was my first venture into a relatively large multiplayer community (compared to Russian FL servers at least). I flew around, explored, RPed, etc., and everything seemed so new to me. Basically, that's what a typical newbie experiences when he goes online. It was fresh.
Eventually I started looking forward to 4.86, because it promised a lot, mainly the storyline changes and full-blown Gallia (believe it or not, but having those sealed jumpgates kind of felt wrong at that time). We could discuss the advantages and drawbacks of 4.86 and 4.87, but I still believe that simply reverting to 4.8x (x<=5) isn't an option.
If I were new to online gaming and Discovery in general (which was the case in 2010), I'd probably be enjoying the mod now (although the player count has decreased twice, I think). But many people have already spent quite some time here, so...
The general idea is that with time people's interest just burns out. They tend to miss the good old days, when the grass was greener, the rules were harsher and Gallia was smaller. Don't leave people's interest out of the equation. Now, I do salute the devs for their continued support on this mod and the effort they put in its evolution. But to truly reignite people's interest it would take more than just Discovery 4.87 or 4.88... Something along the lines of Discovery 2.0 would be in order.
Now, what do I mean under Disco 2.0? I honestly don't know the answer to that. It might be a jump 80 years into the future as someone suggested... Or a couple of hundred years into the past... Or the exploration of some other sector... I wouldn't even mind Discovery: Gallia (with 4.86 Gallia, which could house the entire server population).
Of course, it's easier said than done. I'm not asking people to do it, nor do I have the skills and time to contribute to an endeavor like that at this point (diploma paper and all). I could learn how to mod FL in the future though, should the need arise. But mind you, I'm just a random forum lurker who no longer plays or cares about his ships (which have been given to various people long ago anyway). A radical change would require a server wipe, and that as might be the final nail as well.
Oh, and speaking about the community... No, I actually won't say too much bad stuff. It's just that people take the stuff which is going on here too seriously sometimes (which in worst cases leads to open hatred). But still, comparing to some other communities I've seen, Disco GC is like a big family (with some issues, of course, but that's beside the point).
Well, it looks like I've produced a tl;dr wall of text. In conclusion, I'd like to say that Disco has been extremely fun while it lasted (for me, I mean). I had my share of RP, PvP, faction leadership, etc. I do wish the community and the developers all the best and hope that the community gets through it. If not... well, all good things come to an end (and Disco is definitely good). And thanks if you've made it till this part of the post.