A digital version of the Collector's Edition hasn't been mentioned, either. That doesn't necessarily mean there will not be one, or that if there is there will be no way to upgrade.
I would assume Larian will provide more details at least when pre-orders for digital version are announced (for GOG, etc), if not sooner (maybe next kickstarter update, or something).
Maybe there is still stuff to sort out before they can confirm anything about the possibility of upgrading.
