I'm actually surprised that so few people have understood the real motive.
It's so that he can have (unlimited) power to achieve immortality.
It's not about killing Jedi, or establishing order, or just wanting to be on top, or the EU reason about organizing against the Vong. It's just greed. The Sith are attached to physical life and will do anything and everything to maintain it.
The Plagueis novel has been decanonized, yes, but Plagueis the character still exists and the Tarkin novel + what we know of him from RotS still indicates that he was searching for immortality. Palpatine could never let his master achieve that, since that would mean he would not be able to kill him and take his place as Dark Lord of the Sith, so he killed him before he could discover the secret. I don't think it's coincidence that he temporarily had an alliance with Mother Talzin and the Nightsisters, whose "magicks" are able to let them assume ethereal forms or that he is funding the research of Dr. Cylo, who has a sort of AI program that lets him replicate his persona across multiple bodies in the event that one dies (even if that's not true immortality).
The Tarkin novel makes it explicit that Palpatine does not care about the Empire as a thing in itself, or the ideology of it. He uses it as a means to an end for ultimate power. With the Empire, Palpatine was able to wipe out the major threat to his power - the Jedi - so that he can spend all his time studying the dark arts in his pursuit of the ultimate goal. For most of the book, when he's not dealing with the Imperial Ruling Council, he's meditating in the ancient Sith shrine beneath the Jedi Temple trying to coax out secrets of power from the dark side.
Tarkin said:
Vader looked down at him, the sound of his regulated breathing diminished by the howl of the high-altitude wind. “Moff Tarkin should be ordered to return to Sentinel Base and resume his duties there.”
“Ah, so you’re arguing on Tarkin’s behalf, are you?”
“For the Empire, Master.”
“The Empire?” Sidious repeated, miming surprise. “Since when do you put the needs of the Empire before our needs?”
Vader crossed his gauntleted hands in front of him. “Our needs supersede all, Master.”
“Then why do you contradict me?”
“I apologize, Master. I will do as you have commanded.”
“No—not good enough,” Sidious snapped. “Of course you will do as I command, and of course Moff Tarkin needs to resume his duties on the Sentinel moon. The sooner the battle station is completed, the sooner you and I can devote ourselves to more pressing matters—matters only you and I can investigate and that have little to do with the Empire.”
This doesn't come as a surprise since Luceno, the book's author, has said he wants to do a novel about Sheev has and that he thinks his goal is achieving immortality to essentially become a god over the Force.
The EU had the immortality concept as well with Palpatine's clones on Byss, but I think the goal in the new canon is more obviously to just flat out never die at all. I think this will become more obvious in the post-RotJ period since it will be almost unavoidable to mention that there was no proper chain of command since Palpatine never intended to die.
In short, I would argue that both the Empire and even the concept of the Sith itself are not things Palpatine had true loyalty to. He created the Empire purely so that he could get the power he needed to accomplish the task of understanding "the great mystery", as he called it in RotS, and the Sith Order was likewise simply a path to that power. Palpatine abused the Rule of Two as it was, so I don't see any reason to believe he truly had loyalty to Sith ideology. He was always in it for one thing - himself.
