Initially, it's sure to lower the number of CMDRs in Open mode. Primarily because nobody enjoys waiting for a pad to dock in at the engineers. Solo and PG will be the best options for that.
After the rush on engineers, who knows? I suspect it'll be about the same as it is now. There's nothing compelling in 3.0 to bring people into Open.
C&P seems like a specific device to encourage players to return to Open.
Engineer updates seem intended to make and effort to balance the playing field for modded ships.
Will it work?
Will there be a significant change in population distribution between the modes?
I imagine people will find excuses to stay in solo.
I imagine people will find excuses to stay in solo. But that being said I do think less people will be turned away from open play and CGs in general now that gaining quality enough modules to defend yourself is less of an issue.
Though it is still an issue.
The initial engineer unlock requirements are still nothing but roadblocks for many players trying to achieve the ability to defend themselves. But that is what the Fdev gatekeepers still seem to want...
You want combat armor? HAHA go mining...
You want to go fast? HAHA go to basically the center of the Galaxy to unlock Palin/Farseer
You want Shields boosters? Give me my liquor that you can only carry like 5 of at a time. HAHA! (Rinse repeat for like half these smucks.)
Oh you want to know where to find mats? haha thats your job silly! why would the devs put this info in game lol? You players need to create a website that still poorly explains things to a lost noob trying to figure out which way is up in this system.
Until these requirements are looked over again the "problem" will stay far from solved.
Will 3.0 Increase, decrease or have no effect on Open population?
C&P seems like a specific device to encourage players to return to Open.
Engineer updates seem intended to make and effort to balance the playing field for modded ships.
Will it work?
Will there be a significant change in population distribution between the modes?
In the short term the release of a new version may bring more players back to the game in general, making Open (and PG, and Solo) higher in population. 2.4 certainly did.
I doubt it will change the ratios between the three modes. People who play Open-only or Solo-only because they want that type of gameplay won't see any reason to change their mind. C&P will not significantly affect the danger level in Open in most cases ... Engineering will make it even easier to make an invincible ship, but that was already practical with minimal effort because of how early Felicity Farseer and Lei Cheung are on the unlock tree. So I can't see the people who would play in Open if it was perfectly safe but won't play in it if it's only perfectly safe for a ship with a proper shield changing their minds. (Are there actually any such people, or do people just claim there are?)
In the longer term, if payouts are similar to Beta, I expect a move from Solo to both Open and PG (possibly more to small PGs) because certain wing missions will be extremely well-paying...