Yeah, I'm not sure why anyone would think a great core game at release and having mod support are mutually exclusive. CDPR don't strike me as the sort to publish an unpolished game, hoping that modders come to the rescue. Not even close. Besides, W3 had mod support and I didn't see any issues there.
Mods are usually tweaks, enhancements and additions rather than fixes.
This is the overall approach. Right now, rather than worrying about, "But, if we decide to build this section of the game this way...how will that affect modding?" they're focused on, "We need to make the single-player game as solid as we possibly can."
If modding can be added in later, I would guess it probably will be. If not, well, that's the way the cookie crumbled. Time will tell!