I think that Frontier is trying to achieve that at least with the mission system where the missions are ranked not rank gated. Pick an elite mission and be prepared for some elite npcs. I don't think it's quite working right but it seems to be the intent.How about letting players choose their own difficulty level? How about increasing payouts/rewards with increasing difficulty levels?
Those who don't want to constantly fight can choose a low difficulty level and those who want a challenge every time they encounter an NPC can choose a higher difficulty level. Blizzard did this decades ago with Diablo, with further refinement in Diablo 3.
Would it be a pain to program in difficulty levels? Maybe. Would it quiet everyone's ing? Probably.
I'm not much for combat myself but I don't see the need to fall back on the AI. Frontier should have seen it coming with giving mods to npcs when it would take some time for most players to get there but they fixed that fairly quickly.
Interdictions just need some tuning in terms of the frequency and npc rank. I think I'm seeing way too many elite pirates when my combat rank is competent and I have no missions or cargo except for a few reward commodities but it's not hard to deal with them without their mods.