You don't need a 1 for 1 Heir to the Empire. You can change it to fit the current age requirements. It would still be a WAY better story than the sequel trilogy. People are more understanding of age related changes than changes because someone thinks they can redefine Star Wars.
I will categorically disagree that no one wants Mara Jade. Luke remaking a Jedi order that allows attachments 100% fits with what we know of Luke's character. Seeing Luke marry another force user and allow such attachments would be in line with his character.
But it's not just later characters. The Revan and Bastilla storyline is better than anything Disney has made. There's so much to draw off of with the expanded universe. Giving us Rey, who lacked almost any agency and never encountered anything she couldn't do was a huge disappointment.
This is the problem, people confuse attachments with sex. Luke had attachments. He wasn't anti-attachment. He believed his attachments were with everyone he cared for. Han Leia, etc. Love can be more than sex. People wanted Luke to **** because they saw themselves as Luke and fan inserted them into him and he wasn't ****ing he wasn't a man. Luke is a highly religious person, celevacy in priests, eastern monks, etc. isn't uncommon.
So let's talk aging it. Fine just for ****s and giggles. Let's stick major plot points.
Stuff that won't be hard to age up - Characters existence not hard. Doesn't really make sense for 70 year old han to still be an active fighter and not take more of a dodanna type of role, but whatever.
Events: I find it hard to believe Thrawn could keep the remnants of the empire together under the empire banner for 30 years. The reason the first order kind of works is it's a new political and military power. I mean you could explain it by saying the empire was never officially destroyed just pushed to the outer reaches of the Galaxy but how does that not spit in the face of star wars?
Finally from a storytelling standpoint not aging it up it would be horrible.
Movie one is about establishing the villain, not the worst thing. Thrawn and his remnants get force disrupting salamanders to overtake a palatine cloning facility. A clone of a Jedi master offers to join him if he lets him take Luke and Leia as acolytes. Thrawn continues to grow his empire, Luke and Leia and co are secondary in this. BTW thrawns biggest threat isn't Luke or Leia, or Han, but Admiral Ackbar.
Second movie is about putting the heroes on their heels. Hey first we start the movie off introducing something that never has existed in star wars, an automated fleet of ships from the Clone Wats era. Suremakes sense the empire never went down that path as they devalued human life, but it doesn't make sense for it's creation then when they couldn't have an X Wing that needed only 1 pilot but hey this isn't ****ting on Lucas's legacy. Thrawns makes clones and uses a religiously enslaved people (Nogrhi) and gets gains. But needs Katana fleet. Luke and Leia rescue the person who knows it's location from Thrawn but Thrawn still gets the fleet.
third book. Thrawn uses invisible astroids (lol) to cripple New Republic capital coruscant, NR forces try to press the advantage by attacking a ship yard to get a device to find clocked asteroids, while Luke and Leia go to destroy the cloning facility with the now religiously attached to Luke and Leia Nogrhi. Thrawn dies not by hands of Luke, Leia, Han, or any other protagonist, but by Rukh his Nogri assassin.
Yeah that sounds so good.....
What makes the books good is that Zahn is writing Thrawn books, books about an interesting villain, his takes on the heroes is bad. Like really bad.
They have pulled from the EU. Thrawn ported and honestly ported better than I expected into canon via Rebels and Ahsoka. Which allows him to be a threat and not be around in the OT era. There's other examples I won't get into. But one thing Filoni and crew have done well is pull from history while still moving the story forward.