I've seen a couple of people proposing a possible compromise for the Solo / Private Group folks, as an alternative for Open Only, and to be honest it seems like such a good idea that I feel like I should do my part in promoting it!
One of the main arguments in favour of Open Only is that players operating in Solo are essentially untouchable - they can do their thing in their own little instance, and there is nothing that anyone in Open can do to stop them. But what if it was the other way around? What if players in Open
could perform actions that would count against the efforts of players in Solo, but players in Solo could
not counter the efforts of players in Open?
For example, you're making great trades and increasing your power's bar in the system. The contesting power wants to slow your progress, but you're in solo, so can't attack you directly. BUT, your actions also spawn other NPCs from your power to also trade in their instance, and they can stop them. This will slow down some of your progress if they destroy them.
So if you needed to deliver macguffins to somewhere in order to bolster your Power's hold on a system, you could either do it in Solo (and no doubt reach your destination safely), or you could do it in Open (in which case other players might potentially be able to stop you). But if you do it in Solo, your actions could then be negated by other players hunting down the NPCs that represent you, giving them a way to actively oppose you... whereas if you made the journey in Open, your contribution would
definitely count, as long as you actually reached the station and delivered the macguffins.
Thus:
A player making deliveries in Solo can be countered by another player hunting NPCs in Solo;
A player making deliveries in Solo can be countered by another player hunting NPCs in Open;
A player making deliveries in Open can be countered by another player who
hunts them down in Open;
But a player making deliveries in Open
cannot be countered by a player in Solo!
In essence, this would turn the current 'balance of power' on its head - rather than Open players being at the mercy of their unseen opponents in Solo, the Solo players would be at the mercy of unseen opponents instead. This would quite naturally encourage Solo players to try playing in Open, so that their actions could not be undone so easily... it would not require any contrived incentives or anything, players would just gravitate towards Open as the most efficient choice.
It's such a simple idea, but it's so elegant... and I can't see a reason why it wouldn't work!