Final Fantasy VII Rebirth producer Yoshinori Kitase alleged that a potential remake of Final Fantasy VI would require double the amount of time the Final Fantasy VII remake is taking, which is roughly 20 years.
Naoki Hamaguchi, the director for Final Fantasy VII Rebirth, and the producer Yoshinori Kitase committed to a 45-minute interview with a French YouTuber, and a rather interesting note about a potential Final Fantasy VI remake was made.
Kitase mentioned that a remake for Final Fantasy VI would require twice the amount of time that the Final Fantasy VII remake is taking, which would be roughly 20 years. This is likely due to the game being more vast and rife with content (even though a lot of content was taken out with the Final Fantasy VII remake).
In a conversation with other team members, various other staff of Square Enix were in support of Final Fantasy VI getting a remake, but there is currently nothing planned for the classic RPG (as noted in the interview).
Some are wondering if perhaps the 20 years is taking into account other projects that Square Enix might be working on, such as possibly other Final Fantasy remakes.