I believe that forced grouping IS the answer. Solo questing is a serious detriment to recent MMOs. Between the extremely active gameplay and the ability to solo your way to level cap you end up with mechanics that are inherently antisocial, creating this bastardized genre of 5000 player games that have less player interaction than a coop diablo game. If you want to group in a quest focused game you have to be in sync with each other on quests, you have to find players that aren't playing the game like a single player rpg, you have to fragment the gameplay into meaningless public quests and instanced dungeons, you have to homogenize class design so that everyone is self sufficient and can dps and you have to remove any spells or mechanics from your game that allow players to interact with each other in any way.
Other than accessibility to more types of players ($$$), what is the point of allowing soloing in an MMO? So that you can play a bad pseudo single player game where you see other players running around instead of one of the many great actual single player games? So you can solo to level cap and THEN group? In that case, leveling is admittedly busy work that you're suffering through to get to the grouping end game. Easy soloing to level cap is one of the major reasons why MMOs have largely meaningless leveling experiences and all the 'good' content is loaded into end game. Why not build a game where it's the style of gameplay that you find at level cap right from the start? In TESO's case, something as simple the Cryodiil style gameplay starting immediately at level 1 and being the main play style would be a huge improvement. Hell, even the anchor public quests are so hidden and understated that no one in my group even realized they existed until around 4-6 hours into the game.