[knowom]

You can also provide solo content instead of resorting to allow for multi-box. Developers could do a lot more though to make better solo play options without resorting to allowing boxing. How they choose implement them is up to the developers of course.

NPC's that buff players
1 use pet summons of different class types with built in duration times.
Follower quests where you help protect a given NPC class type.
Better use of potions and applications of them. They could have reuse timers built into them on a case by case basis.
Could reduce down time between fights.
A lower amount of zones in total so players have a greater tendency to group and do so more quickly and easily.
Special zones quest access that requires from 2 to 6 players via a quest for access and lacks camp safe spots at least to do anything worth while within them loot wise.
Could use linked mob pulls to have access based on the amount of players around at a time while still allowing for solo play or limited group size play.

That's just my initial thoughts on different ways to get around boxing while allowing for plenty of solo play, but find ways to encourage grouping even if it's smaller more limited group size it could be scaled based on the size around at a given time.