The Other Darrin: In the animatic uploaded by Mike Milo, Flavio has a completely different voice. This is because his creator was to voice him. In the end, Rob Paulsen was hired to do his voice.
What Could Have Been: A full series. It's also a shame because in the old production blog, we can see that Mike Milo has worked really hard on this and even has additional information about the character(s) that may not be revealed unless you've been lurking in the blog entries.
The comments that can be found on this video, even the recent ones, sometimes contain pleas or requests that he should make it into a series