Would not restricting solo from crossing over to open simply further provide a disincentive to players playing in open? It seems to be honest the issue isn't that there aren't enough players who want to engage in PvP duels (which their may not be, but forcing open play won't help that), as they will come into the game more so with the ability to swap from Solo to Open (I'm almost exclusively solo now as that were the most fun in the game is for me (while trading and exploring the populated galaxy the last thing I want is someone interdicting me and killing me for the LOLs, sorry I have no intention of being your punching bag), but that doesn't mean I don't want to try some PvP combat at some point (which I fully intend to do), but I don't think I would bother creating a new character to do so).
The real issue is that there is a lack of unwitting human players to prey upon, which forced open only, or limiting characters to be in one or the other might provide as players who want to participate in the open universe in other capacities (such as PvP duels) are forced to play gazelle to your lion.
Exactly. I play in open, in an unarmed courier no less, and I do so because I like the sense of danger doing this provides. Being an unarmed courier, I'm also no match for anyone in a fight, but I've designed my ship to be able to flee rather easily.
That having been said, I have no problem playing the victim to someone playing a "bad guy" if they make the effort to make it enjoyable for me. Even a little roleplay would be sufficient. Sadly, past experiences in games with open PvP have proven that most "bad guys" have zero interest in actually making it fun for their victims. In fact, there are far too many who go out of their way to make it as unpleasant as possible. Thus, while I may be playing open, if player-killing (as opposed to proper pirating) became frequent, to the point the game is no longer fun, I'd go to solo and enjoy my game slightly less, as opposed to stay in open and not enjoy my game at all.
If I'm ever forced to choose between open and solo, I'd choose solo. And I doubt I'd be alone. Many of the people who play open do so because they have the option to drop to solo when they feel like it. Force people to choose, and most would choose solo, and open would be even more deserted than it is now.