The Marvel Cinematic Universe as a franchise is on a hot streak. Every movie that 's been released over the last couple of years has been a major hit, either with fans, critics, or both. However, it wasn't always that way. There are a handful of Marvel films that are generally agreed to be, at the very least, on the lesser end of good, and most would place Thor: The Dark World in that category.
One person who has been more than honest in the past about his opinion of the film is actor Christopher Eccleston, whose opinion of particular importance because he was actually in the movie. He played the dark elf Malekith, the film's big bad. He's made it clear in the past that he didn't have a great time making the film, which makes a bit surprising that the actor says he might be convinced to return to the MCU.
Although, in Christopher Eccleston's recent appearance at New York Comic Con (via RadioTimes) he does put forth one significant stipulation he would have for a theoretical return. It's all about who would write his return. Eccleston told the NYCC crowd...
If it was the guy[s] who wrote the third.
For the record, Thor: Ragnarok's screenplay has three credited writers. Eric Pearson, Craig Kyle, and Christopher Yost. While Taika Waititi did direct Ragnarok he did not have a hand in writing it. Thor: Love and Thunder will be written by Waititi, so technically, the guys who wrote the third film aren't writing the next one, so perhaps Christopher Eccleston won't be interested.
The reason that Christopher Eccleston would be interested in potentially returning under new writers is because he, like many fans, much preferred the tone of Ragnarok to The Dark World. He told the NYCC crowd that he felt The Dark World lacked humor, and that certainly wasn't an issue in the most recent Thor movie.
There's also the minor issue that, within the MCU, Malekith is dead, having died at the end of The Dark World. But these are comic book movies so that's hardly a big deal. He could always be brought back. Alternatively, Eccleston could play an entirely different role. He mentioned at NYCC that he wasn't a fan of sitting in the makeup chair for hours, so he'd probably prefer that. And the fact that we've never seen the actor's actual face in the franchise would make it that much easier for him to appear that way now.
Christopher Eccleston is a great talent and the fact that he was basically wasted in the MCU as one of the more forgettable villains, in a franchise that doesn't have many memorable ones, is a crime. I for one would love to see him come back in some capacity. As the MCU continues to grow, the possibility of seeing familiar actors return in new roles only increases, so perhaps something like this could really happen.