Hello Petar,
thank you for your question.
We have been thinking about the the dungeons systems and they will be scaling with your progress. All dungeons will require 5 man group, maybe some will require 3 people, but none will allow 1 player to complete it. To enter the dungeon you'll need a group.
Solo progressing will be done by completing quests and doing PvP(with others)
MMoRPG is multiplayer genre and it is meant to be played with others.
Kind regards,
Armegon.
Guys, maybe you should consider solo PvE something like Albion Online has some smaller expeditions for 1 player where he/she can get much better items but still not the best ones like in raids.