After Miura passed away, the Great Berserk Exhibition added a space at the venue that features a reproduction of his desk, a video message he had recorded (originally only meant to be broadcast once, for a select group on the opening night), tribute artwork from other mangaka, and 12 color illustrations from an animation project he had secretly been working on with his friends.
We've already made a post about the giant robot animation project, on which we unfortunately have very little detail. We're still on the lookout for more.
That aside, there is also some Sci-Fi concept art laid out on the desk area. It's unrelated to the giant robot animation project, and is instead something Miura did in the early 2000s. He produced four illustrations at the time and they were published semi-anonymously in a doujinshi released in December 2004. His name was only indicated in reverse (think "urotanke raumi").
That concept doesn't have a name attached and there's no indication more of it was planned, but I'm sharing it with you because I think it's a cool glimpse of what a Miura science fiction series could have been like. Please excuse the quality of the photos, as I didn't want to damage the book while taking them.