10M potential players in 2 separate games combined, maybe. As things stand now I rarely can see more than a handful of random players (people who are not on my friend list) on an average day, and even that only if I happen to visit some of the popular systems.
Steam peak concurrent players at the moment is around 5k? -ish? Let's roll with that. Let's double it, to cover all platforms. Let's ignore for the moment that Horizons and Odyssey are for the moment split. (yeah, i'm being a bit all over the place here, but think it will suit to illustrate the point). I'll leave consoles out of it though, just consider PC.
So, 10k peak.
A good proportion of players are explorers, many of those will be out in the black. Let's assume 20% of the people playing at any given time are not in the bubble. I'm not sure how busy Colonia is either. Let's say that 20% includes Colonia people as well.
8k in the bubble?
How many systems in the bubble? I understand the number is around 25k.
Of course, some systems are a lot more popular than others. Let's assume roughly half are in systems where people rarely go. Whether its because they are wandering, or have set up their homes there, or they are running missions that are leading them there at the time.
4k in systems which are somewhat frequented by players. How many systems does that cover? I'd guess we are still talking literally thousands. Player groups working the BGS, Powerplay systems. Systems around SD and engineers. Systems with other special features.
Let's make it a nice round 4000 systems that are somewhat popular.
Where does that leave us?
Approximately 1 person per system at any given time.
At this point, does it even matter if that "average" person per system is in Open, PG, or Solo?
And that's before we get into the fact that within systems there are many discrete locations where if someone else is at you won't see them anyway. If i'm at Station A i'm not aware of person on Planet Z. Or if i'm in SC i don't know that someone is doing a CZ in the same system or bounty hunting in a RES.
Even when i'm playing in open and i see friends also in open even if they are in the same system, i might not see them at all, or maybe briefly.
So, when you look at it like this, anyone who thinks that making ED open only (or incentivising open) would change their experience much, they aren't really thinking it through.
By all means, play with the numbers, be more or less generous with some of the estimates. Its not going to make that much of a difference.
The only place where you might see some difference is the really popular systems, or CG systems, but those places already have lots of people in them, you already see people in them, and when it gets too busy, new instances spawn anyway, so more than a certain amount, you're not going to see more people anyway.
Food for thought?