Sorry, but I don't see the reasoning behind adding more to the game or post epilogue content, when it's core could use so much more refinement/improvement. The game is already one of the most massive titles on the market, what's the point of adding more and more to it? It's like adding level after level to a house standing on clay...extreme analogy here, but you get the point.
I think that after almost six months of user feedback most negative issues within this game can be summarized as:
Storytelling:
Undeveloped main antagonist(s) and their lack of presence in the game, mid level game pacing, lower quality of the third act and incomplete epilogue, lower quality of Skellige quest content( unnecessary smuggling caches), undeveloped character arcs( especially Yen/Ciri) and presence of the outcome of choices made throughout the series( Vergen, Adda, Anais, Iorweth, etc), Reasons of State quest and it's effects on the world, etc
Gameplay:
Enemy AI, variety and their aggro radius, skill balance and lack of difficulty through mid-later portion of the game, few active skills and little complexity in combat mechanics, poor character progression through disorganized and unimaginative skill trees, cluttered crafting system with either overpowered or useless gear, unrewarding loot/xp system, MMO enemy level mechanics and poor itemization, clumsy soft lock targetting etc.
Misc:
Unbalanced game economy, poor crime system, Roche AI and controls still need improvement, more density in world space in terms of npc/monster encounters and ruins/unique locations, more world interaction, inventory improvements, etc...
I love this game, despite all the flaws... but if by some chance CDPR decides to make a Dlc/Enhanced edition that aims to improve on half of these things, it would benefit the game far more than adding a whole damn continent to existing world.