I don't believe that Outlaw formally announced any firm plan for a product to be more advanced / robust than the 978, only a desire to, at some future point, attempt to have some product that had some of the advanded features that may have been percieved as more esoteric than those of the 978.
A "wish list" for such things will probably be a fun new topic...
Actually, I believe the 998 was annouced first and the 978 came second because of continued Trinnov problems.