Oh clearly manufacturing one is non-trivial, but up until the expiration of the patents it would have been difficult for anyone to even consider designing & manufacturing a new multi-gear unicycle hub without risk of patent infringement.
At the price that people are clearly prepared to pay (well in excess of $1000 for a used hub), and the explosion of interest in unicycling, perhaps now a company might start thinking about it.
Or perhaps Florian will have success soon with finding a company who they can partner with to produce future hubs.