Sadly, it seems the story already has the same sense of urgency Oblivion had. So to ignore the MQ will require the same "efforts".
I think the mainquest will follow this:
1- Character creation in prision. (First Quest)
2- Asked to be one of the Dragon Hunters (Dragonborn) (Second Quest, now starting from this moment you will be able to do whatever you wish to, and there won't be any sense of urgency.)
3- Dragonborn training quest lines. (A series of minor quests, this will also not have any sense of urgency and still give you the freedom to do what you wish.)
4- Some twist. (The sense of urgency starts here.)