Well my experience in CG shows that: Combat Zones are more profitable (and enjoyable) in solo than in open - no problem with that. Just in Lugh, combat farming in solo allowed profits at least 4 times those in open. The problem arises in a scenario like the following one: commander X and Y have the same ship. X plays in open and is struggling to afford good weapons/shields/engines. Y goes to solo, farms and then come back to open with a better equipped ship in the same time. I think this is not fair.
Another example: faction A (I'm talking of players group that do role playing) tries to blockade a space station where faction B tries to deliver some cargo. Players in B pass to solo to elude the blockade. The result of the CG is therefore independent from the effort by faction A.
it seems that the problem is related only to CGs anyway, so probably that is what should be fixed and not the modes of play.
While I agree that CG present their own problems and DO need a solution, stopping mode changing to fix it seems like taking a sledge hammer to it... and I'm not sure it would totally solve it anyway.
But as to your more general objections:
"commander X and Y have the same ship. X plays in open and is struggling to afford good weapons/shields/engines. Y goes to solo, farms and then come back to open with a better equipped ship in the same time. I think this is not fair."
And:
"faction A (I'm talking of players group that do role playing) tries to blockade a space station where faction B tries to deliver some cargo. Players in B pass to solo to elude the blockade. The result of the CG is therefore independent from the effort by faction A."
With the first objection you need to bear in mind that player Y, instead of going to solo mode could just as easily go to a less 'player intense' are of Open and do exactly the same thing. Which raises the question, how would you even know HOW a player came by his credits? Besides this there is also the great big fact that player X can ALSO go into solo and do exactly the same as player Y. You see, it's all about choice. Both players have the same choice and it is up to them how the exercise it. But what they should not do is to try and limit the choice of another player just because it is contrary to the play style YOU choose.
With the second objection, this is much simpler. Player blockades are impossible BY DESIGN. Even if this were not the case, preventing player B from switching to solo would not solve anything. The instancing system alone makes player blockades just as impossible.