The problem with that is with players running their own mod-able servers, I think they'll start losing out on ship sales, a huge part of their income at this point. So why I don't think it's out of the question, I don't think it will happen until closer to Star Citizen's end of life.
If they ever changed the plan about quitting ship sales on launch, I sure missed that. I mean, I wouldn't be all that surprised if they wanted to keep doing that once they start running the game for profit, but at the very least I think that's still the plan. Just a couple days ago someone asked on Spectrum how long you got to apply the CCUs, and every answer was still 'until beta.'
Besides, being able to preview ships on a private server with like dozen or so other people isn't really all that different from IAE events, they just stop being time limited. I don't really think that'd cut into sales, heck, it'd probably encourage sales. The main universe is after all where the whole MMO is happening, private servers are just that, private. You wouldn't buy a Porsche just to keep it in your garage for your wife and kids, and the occasional visitor, to gawk at.
So all in all, there's really no downside to releasing private servers even right at launch, though they're probably way down the priority list so we'll probably only see them a year or two after.