Obviously late to this party (I've been meaning to post here forever and keep forgetting). Anyway here's my few cents.
As a leader of a large BGS group (both manpower and controlled systems wise) I personally wholeheartedly support the notion to reward players more for playing in Open - when it comes to both BGS and Powerplay.
But I think the bonus should only affect the outcome of player actions, rather than any cosmetic items or Arx. And in fact rather than a bonus, it should be reduction in outcome value in PG/Solo. Why? Because while Elite is a competitive online game - especially when it comes to BGS and Powerplay! - there are legitimate reasons that someone may want to play in PG/Solo. Be it disability, age or whatever else.
By introducing bonuses for Open play, we would be taking the opportunity to earn those bonuses away from the people that are not really in a position to play in Open. By introducing reduction to PG/Solo actions, we still allow those people to participate, while keeping the spirit of competition for an online, multiplayer competitive game.
50% reduction would be fair I think. So people in Solo still contribute, but on a large scale it doesn't make sense to go Solo overall.
Honestly, I personally find this sort of change to be the worst of both worlds. Going completely open only does exclude most players, but at least it does it cleanly.
One could imagine a situation where one side has 10 players and the other side has five, one of whom is a practiced ganker.
The 10 players, playing in solo, find themselves unable to keep up with the five players, because of the Merit disadvantage. As a result, they try playing in open, but that single practiced ganker is able to kill enough of them effectively, due to the massive Advantage PVP has over hauling ships.
Because of one player, 10 players are unable to effectively influence the game. Pvp has become the single important choke point which controls all others.
It would have been better if those 10 players were simply rejected from the start.
Now, consider the alternative. There are 11 players, and through concerted effort, they are able to ignore the penalty and win anyway. The other side feels enormously frustrated, and things are no better than before.
Finally, consider the last and worst alternative. Realizing that they must play in open in order to win, but still not wanting to participate in pvp, they throttle their connection, similarly to how people are currently throttling their frame rates to reduce heat gain from the super Cruise overcharge, and avoid instancing with anyone despite nominally playing in open.
Now, absolutely everyone is frustrated. The PVP side are frustrated exactly like before. The hauling side are frustrated at feeling obligated to throttle their Connection in order to win. Pretty soon, nobody wants to play anymore.
Of all options, the Merit debuff option has to be my least favorite.