Total retention of the EU was never a goal. I think everyone would agree that that's kinda crazy.
But there were some great things in the EU. Disney could have gone for like 15-20 years just mining and adapting the best bits of it.
I still get depressed thinking of the really great rogue squadron TV show we could have gotten or the thrawn trilogy of movies.
Speaking of making movies out of the Thrawn Trilogy, who would have made good picks to portray the new characters? Thrawn? Mara Jade? C'baoth? Karrde?
The truth is that even in the mid-'90s, the OT cast was visibly too old for a live-action Thrawn Trilogy adaptation to be easily done. (Consider that Hamill and Ford were both already older than the characters they portrayed in ANH, and then the trilogy that spanned four years was filmed over six years.) Basically, by the mid-'90s, the actors were on average a decade too old; more the age they'd be in
Vision of the Future (19 BBY) than the age they'd be in
Heir to the Empire (9 BBY)
I'm all in favour of adapting the EU (with a bit of stream-lining to cut our or tweak the really-too-hokey stuff) to the screen, but I don't think live action was ever an option.
If they gave me control of LucasFilm and a big bag of Disney money right now, I'd get far away from the bad taste of the current "canon", and instead start adapting the more ancient stories of the EU... as high-budged, high-quality animated series. Put the Jedi origin story on the screen, show the Force Wars on Tython, adapt
Tales of the Jedi and KotOR (both the games and the comics). Not to mention
Knight Errant. There's a whole load of stuff in-between that's been mostly glossed over thus far, too. And then we can work all the way to the last of the great Sith War, culminating in Bane's grand plan.
That would be many years' worth of material, right there.
After that, who knows how good all this 3D, deepfake, neural net, what-have-you stuff will have gotten? Maybe by then, something that
looks exactly like a live-action version of the post-RotJ EU could be put on the screen. And then you can put book-only characters on the screen
precisely as you imagined them.
But if that's not workable, if it still gets you 'uncanny valley' results, then it's just as possible to adapt the post-RotJ EU in an animated format, too.
After all, even today, you have people adapting
Heir to the Empire as a fully 3D serial, and while obviously not "real studio quality", it's very impressive, and getting better with every released chapter. Look at the recent release (chapter 22) here:
It's only going to get better, as far as "
look at what I can do on my home computer!" is concerned. I think that not altogether too long from now, we won't need a big studio to adapt the EU to the screen. We'll be able to do it ourselves. With even better quality, and with less effort than the current efforts require.