Mistwell said:
The problem is that there are sometimes several dozens of routes to a PRC, which have diferring level requirements. In fact, often if you think you've found the fastest route to a PRC, someone else will come along and give you an even faster one using some obscure feat or PRC from some book you've never read. Not to mention the often disputable methods used to obtain a PRC.
For example, does the SpellThief's ability to steal spells of a high level and then cast those spells count as spellcasting ability in terms of Arcane Trickster qualifications? I've seen good arguments on both sides. And that's just one PRC off the top of my head.
It's a hopeless task...
I don't think so. Most prestige classes are pretty simple, since they use skill ranks or BAB to create the minimum ceiling. Those are easy, and could be done with somewhat generic comments ("Any classes with the fighter attack progression can enter this class at level 6").
What you are left with are those classes designed to require multi-classing before you enter the class, or those that have abilities to set the minimum level (usually some sort of spell casting class). Some just require legwork (probably easiest if you limit yourself to a set number of products, WotC products would be probably easiest to start). Others could have commentary about argued points (the "Precocious Apprentice" feat has been argued to allow you to enter
Mystic Theurge at 5th level, or "The militia feat has been argued to allow you to enter Eldritch Knight at Xth level").
Now, as I mentioned above, opening it up to all companies would more than likely be a headache. However, starting with WotC would give you some finite options. After that the list could potentially be expanded to the major companies products, possibly.
If I were to start doing something like this, I'd start with WotC products. In classes where it mattered, I would likely have a category for "core only," " all products" and "disputed points" (which I doubt would be too overwhelming, but I could be wrong).