Too little too late. To make that work, it must work right from the start.
IMO the problem was that they didn't think it was necessary to have a system (that works), exactly because the original idea was more like "we came up with the concept of PrCl, but it's probably too awkward and few people will use it, so we present it as an optional DM-DIY tool". They did something similar with custom classes (see the Witch example) but people largely ignored that option, and designers also used it only a few years later and not in the same magnitude as PrCls.
I don't buy that they didn't think PrCs would be used much, given the splatbooks which came out almost immediately after 3E were stuffed to the gunnels with them.
I might be wrong of course, but basically what [MENTION=1927]Thaumaturge[/MENTION] says above is the same that I seem to remember Monte saying about PrCls.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.