BIZ points out that Smith does not currently have a go movie lined up while Tommy Lee Jones' involvement remains uncertain. Variety surmises that it's unlikely the studio would greenlight the project without the duo's involvement.
MIB is one of the most successful comedy franchises of all time. The first two films, which were released in 1997 and 2002, combined to earn nearly $1.1 billion worldwide.
The studio is eyeing a 2010 start date and could go as soon as the spring.