On the website Lego Ideas, there's currently a Lupin the 3rd project to try and release an officially licensed Lego Lupin III set.
https://ideas.lego.com/projects/99030If you're unfamiliar with Lego Ideas, it's a site where people pitch ideas for Lego sets and if they reach 10,000 supporters, Lego will consider making an official set based off it. If the set features an existing intellectual property ie. Back to the Future or Doctor Who, Lego will then contact the owner of the IP to seek permission to create an official set. Also how the idea appears in the project wouldn't be how the final product would look like, if Lego were to produce it.
If we help the project reach 10,000 supporters, then its possible for Lupin III to receive an official set. Any other Lupin III projects that are on the site, if they also reached 10,000 supporters, it would possibly give more chance of Lupin III being considered by Lego. An official Lego set would also help promote the franchise to more audiences.
So if we try our best to help out, there's always a possibility that Lupin could be available in Lego. I also encourage fans to create their own Lupin III project ideas to submit to the site. They could be based on any of the TV series or Castle of Cagliostro. We could create a separate thread for Lupin III Lego Ideas projects.
On a side note: for anyone concerned that Lupin III might be rejected on the basis of its themes, before an idea is submitted to the site, it's first reviewed by the staff to see if it meets the guidelines. As long as the project was based off either the TV series or the second movie, it should be fine.