Yeah, I would say there´s no real connection between the PQ4 and the Furman. They are just two parametric EQs among the hundreds out there, and there isn´t much to clone or protect in that regard. The real issue with doing rack units in pedals is size and price, not many guys would pay $750 for an EQ pedal built to the same studio pro specs as the rack units and it might be tough to keep those circuits sounding the same when shrunk and/or not being mains powered.
As for why they don´t make it anymore, there´s probably just not much of a market for it. Take away the small set of Dimebag fans that use parametrics for boosting and there´s just not much there in the guitar world. Boss has dropped tons of products from their line over the years.