I don't believe there would be any issue with Disney issuing the original theatrical cuts of the trilogy in the future - unless there are any complications with Fox.
Eight years after Stanley Kubrick passed away, his later movies were released on home video in their theatrical aspect ratios - something that Kubrick would not permit during his lifetime. But with the passing of time, with the larger presence of widescreen televisions and with a clear public interest in seeing the movies in those ratios, Jan Harlan and the family consented to the releases.
There are certainly interpositives and masters that exist for the Star Wars trilogy that have been carefully preserved by Lucasfilm, so the inclusion of the original cuts would be something that Disney could do inexpensively as a bonus in their marketing of future Blu-ray releases. As I said before, I wouldn't expect Disney to spend millions of dollars on such a project. If anything gets an 8K mastering in the future, that will be the last version of the trilogy that Lucas approved in 2011. I also can't picture Disney funding a project wherein they take the original cuts and spend millions on VFX cleanup, when they already have the 2011 version with those effects already cleaned up.
It's interesting to speculate what Disney might or might not do here, but expecting them to spend more than a minimal amount is simply not realistic. I wasn't trying to be pessimistic in pointing out that a good 2K scan of the original cuts will reveal issues with the VFX. Just realistic. The final shot of Raiders of the Lost Ark on the Blu-ray is a great example - the matte painting of the warehouse in the final shot is obvious on the Blu-ray where it was not nearly as noticeable on the previous DVD release or the theatrical release. Similar shots in Star Wars and company will have the same issues. Lucas has noted that he cut nearly all of the VFX sequences in Star Wars to be very short shots so that the flaws would not be as noticeable. (There are exceptions - like the flyover at the very beginning, but that was for a good reason) I don't have a problem seeing a version of the movie where the mattes are visible, but I would want viewers to keep the issue in mind so they don't get a bad surprise if Disney ever does issue the original trilogy in this manner.
An 8K scan of the 2011 version is impossible. Every version after 1997 has existed only as 1080p digital video. If they go back to the negatives for a new scan, all the work for the 2004 DVDs and the 2011 BDs will have to be completely redone. Hopefully they go back even further than that and redo all the 1997 work too.