People familiar with the discussions say part of the reason his seat is still vacant is the limited control offered by the 70-year-old label compared with similar roles at rivals such as Yves Saint Laurent, Gucci and Coach.
"Often when a creative director leaves, it is because he did not get enough control," said one fashion communications guru who has worked for big brands including Givenchy, and who declined to be named.
Adding to its woes, Dior's sales growth has stalled in recent months, reflecting a fall in tourism to Europe after the Paris and Brussels attacks and weaker demand in some key Asian markets.
Main shareholder Bernard Arnault, France's richest man, wants a proven quantity to steer the label famous for its cinch-waisted bar jacket, head-hunters and fashion executives say, but the talent pool of potential replacements is small.
A further problem is that most designers are prevented by their contracts from working for a rival for up to a year.
Candidates who have been seriously considered include Alber Elbaz, credited with resuscitating the Lanvin brand but sacked in October after trying to bring in external investors.
But Elbaz was put off in part by the limited scope of the Dior job, having been in charge of everything from collections to advertising at Lanvin, sources close to the designer said.
There was also Hedi Slimane, who was creative director at Yves Saint Laurent until last month. Slimane's track record of seeking to gradually increase his control over every facet of a brand, as he did at YSL, meant Dior could not strike a deal with him either, fashion sources said.
To replace Simons, several people pointed to Maria Grazia Chiuri who currently designs alongside Pierpaolo Piccioli at Valentino, one of the luxury industry's fastest growing brands. A move would make her the first woman to design womenswear for Dior but complicate Valentino's plans to float in 2017.
One source close to Dior confirmed Chiuri was a potential candidate but stressed her name was on a list that also included internal applicants. The source said the hiring process was likely to take some time, possibly a few more weeks.
Valentino and Dior declined to comment.
There is no set formula when hiring a new creative director, fashion executives and head-hunters say. The requirements and expectations vary greatly depending on the brand's size, history and whether it is looking for continuity or a creative reboot.
Dior's desire for someone charismatic and current, with a strong vision but who will be happy to be confined to a relatively narrow role, could be a tall order, several fashion industry sources said, speaking on condition of anonymity.
The Dior job entails designing collections and some accessories, producing six fashion shows a year, giving interviews and representing the brand at events.
It does not extend into revamping boutiques, many of which are designed by Peter Marino, major changes to the Lady Dior handbag or meddling with Dior's advertising for perfume and beauty products, which generate the bulk of its €5 billion ($5.67 billion) in annual sales.
Quitting Dior, Simons said he wanted to focus on his own label and his personal life, but some in the industry say his intellectual and minimalist style did not sit comfortably with the brand's flamboyant image. In one famous ad campaign, a gold-lame-clad Charlize Theron struts through Versailles Palace to promote J'adore perfume, one of the world's best-sellers.
"The problem is that when you are a brand the size of Dior, you have its heritage on the one hand, the designer's world on the other, and then you also have all these many different types of women you want to seduce with the help of celebrity adverts," said a fashion manager at one of the industry's biggest groups.
Soloist vs Orchestra Director
In the past decade, the role of artistic director has evolved from sketching dresses to creating a brand universe that extends into marketing strategies and the shopping experience.
"Before, the designer was a soloist, today he is an orchestra director who tells other people what to draw and what to do," said Ralph Toledano, head of fashion brands Nina Ricci and Jean-Paul Gaultier and chairman of the French Federation of couture, ready-to-wear designers and fashion designers.
Slimane at YSL was the industry's reference in terms of control: he was involved in everything, from ad campaigns he shot himself to the atmosphere of its boutiques to the design and content of the website. YSL is Kering's fastest-growing brand, with annual revenues of nearly €1 billion, roughly half the size of Dior Couture.
Stuart Vevers, creative director of US brand Coach, says his involvement extends far beyond the leather goods and fashion collections he designs, into areas like the image of its stores.
"I still see myself as a designer but I am not sure many creative directors still do," Vevers told Reuters on the fringes of the Conde Nast International luxury conference in Seoul.
Coach's sales and profits rose last quarter.
Some designers lament the fact they have little time left to draw. "Now we have to become image-makers," Elbaz said after collecting a fashion award in October, just days before leaving Lanvin.
"The screen has to scream, baby, that's the rule. And loudness is the new thing."
By: Giulia Sergeti and Joyce Lee; editor: Catherine Evans.