One more point on the unfairness of solo/private group play - I just don't get it (the unfairness bit) - how is it unfair to make game progress in Solo? The only thing I can think of is that you will not get pirated or shot in a warzone by another human player - so it is the other human players who can potentially impede the progress of others that seems to be the issue?
To be fair, I can see the fairness concern. It is safer to grind credits in solo, and there is no downside to balance that, so you can suddenly pop into online with much better equipment than someone who had been there all the time.
I don't think there is a solution though, other than simply flagging any play who enters solo as no longer being allowed to enter open, and I don't think FD will do that.