Life's cruel.
In all seriousness though, I'd honestly recommend Frontier have a look at a way of capping a persons rank. For example, in Warframe, you don't get the super-duper-high end gear unless you can get through the Mastery ranks. Each step towards the next Mastery rank requires a test.
Now, I'm not saying to lock equipment and such; but I am suggesting the following:
First, each rank (for Trade/Combat*) from Competent (arguments could be made for Novice) onward is locked behind a mission (Fed ranking for ex). Passing the test means you rank up, and can progress further. If you cannot past the test, this clearly shows that you have -for the moment- reached your skill cap and this is where the second point comes in.
Second, the NPC difficulty is based on your rank, with a leeway between ranks. Meaning, as a Novice, you could encounter NPC's from Harmless to Expert; each with the difficulties their ranks provide, as well as adjusted bounties (if any). When in a wing with higher ranked CMDR's, the NPC difficulty will be a mixture of NPC's, ranging from one rank below the LOWEST ranked CMDR to one rank above the HIGHEST ranked CMDR in the wing (or perhaps the instance).
* Not sure how it would work for Exploration