If Luke et al do get recast, then angry Star Wars fans will be blaming Star Trek for setting a bad example.
I mostly agree, but then, there is always the chance that SW7 will suck targ balls. Whatever story they come up with, it'll be a challenge to make a new movie properly epic without undoing the victory of the Battle of Endor or introducing a generic even bigger threat!, both of which could feel quite cheap.
The Star Wars movies will be made for casual fans who don't remember what the Battle of Endor was. And they won't have anything to do with the Thrawn novels, they will be new stories.