The Big Solo Cameo was a late addition
According to Wired, the big cameo at the end of Solo: A Star Wars Story, which pleasantly surprised many a dedicated fan, was a "last-minute decision."
*SPOILERS AHEAD*
As it turns out, as early as the final director Ron Howard's arrival to the project of Solo: A Star Wars Story, which was only three weeks before the end of the original shoot, the decision to make Darth Maul the head of the crime syndicate Crimson Dawn hadn't yet been made.
When Howard talked to /Film, the screenplay he was working with "just sort of said 'Boss'" and that no one had decided who the Boss would be. Jon Kasdan, one of the writers, however said that he always wanted it to be Darth Maul.
Article by: Mohammad "Grand Master" Ziad