It seems there is no real wish to consider such a scheme. But there are three other things to consider in the meantime...
1) Collectors making a purchase will continue to have to rely on former owners and their heirs keeping and passing on those extremely rare and easily faked little scraps of paper to know the provenance of an item (uncertain even then unless accompanied by photos) instead of simply looking up its IAR number.
2) Since the huge majority of minor antiquities do not even have the little scraps of paper anyway, collectors will continue to have no real way of knowing if most of the items they buy are really from old collections or from fresh digs - and thus still no way of knowing if they are contributing to the ongoing wholesale destruction of the world's heritage or not.
3) When registration of antiquities does come (and it surely will) it will be forced on us by government legislation - very likely with all the draconian bureaucracy and overkill such laws normally entail, and almost certainly including owner details (bureaucrats love that sort of thing even if there is no reason for it) - instead of being a self-regulated voluntary scheme which would have given collectors an excellent image.
I think Nathan Elkins has highlighted part of the root of the problem on his own blog. I suspect that many dealers have no strong desire to upset the status quo and some American coin dealers (who represent a large proportion of the trade in antiquities) have indeed organised a lobby which actively campaigns not to upset the status quo. Concerned collectors, on the other hand, have no lobby and no organisation.
It is true of course that dealers rely on collectors for their livelihood. But until concerned collectors become a large and organised group with a united front many in the trade will continue to ignore them.