Its obvious that Blizzard has learned little or nothing from the failures of other MMO's. The old formula is LONG past its best by date, and that, more than anything else is why MMO's are in decline.
Forcing people to group has been tried... It failed, and in some cases failed BADLY. There are various reasons that more and more people dislike interacting with other players. Add in simplistic design, and forced grouping, and I'm betting that Legion will see worse drop off numbers than WoD did.
Just about every one of these "sand box" games that have launched for year and years now, has claimed to have some fool proof system to limit ganking. Time after time, its turned out that the fools are the Dev's and the players who believed them.
Gankers can be more creative in finding flaws and loop holes than anyone can possibly imagine. They will spend insane amounts of time and focus to find ways to ruin others play experience. Its a hobby to them.
I wish those involved the best of luck. Past history says they will need it.
In the end, its all about money. What ever model (or hybrid) will make them the most money is what they will go with. Its just a matter of changing player perceptions (in other words propaganda... ^^) to match that most profitable model. This takes time and money, but we are seeing the results all around us.
If you understand developer psychology and corporate politics, you would understand the why of many of the expansions. The Vision™ problem, and in faction/out faction power dictate what gets done, and how. Its pretty much the same in any sector, but with games you get to see the results more clearly.
From my perspective, you might want to try either Star Wars the Old Republic, or World of Warcraft. Both can be played all the way to level cap as solo games. TOR has very good voice acting (for the most part), and its FTP.