I dunno. Given CCP's stance/track record on fixing things and actually doing stuff the players want, I might be better off giving it a shot and hoping for the best.
True enough, especially given CCP's stated priorities for the next 'generic period'*
In any case, a black market, or black markets, really emerge from creative use of already existing mechanisms of transactional exchange - which already exist in EVE. A provided 'black market' would be nice, perhaps - not really black, but real black markets, hopefully, will still emerge due to RPers trying to enrich the fabric of EVE.
Unfortunately finding a way of doing it that is profitable, and thus sustainable, and not dependent on subsidies for the sake of RP, is difficult. That is why it takes an RP motivator to make it happen - rather than a financial motivator.
I think that the OP's idea of a hisec 'fence' corp, or network of corps can be made sustainable, but not as profitable finacially as other ways of spending time, so the desire to do it mainly for RP sake, rather than purely for profit seems necesarry.
*18 months.