For this to work, we'd have to have complete access to all WoTC material in digital format. Not gonna happen if we can't pay a buttload of licensing, but without it the idea is worthless.
Now, I've heard some of you complain (and I know I've complained about this too, bitterly) about the HUGE number of rules floating around. New books, awesome concepts, new feats, better classes, etc. But what to do? It's a pain running a campaign when you have 20 different books to reference to get all the rules right. I'll say it again. It's a pain. It's a real fucking pain.
Every now and then a book will come out that consolidates information other books, like the Spell Compendium. I like it, but there's something to be said about needing a whole new hardback book to consolidate one category of information from 5 other books. Wouldn't it be nice if we could just do that electronically?
There's a lot of good information. The problem is organizing it in a way that's quick and useful. This is the sort of thing computers are designed to do with great effeciency - help organize and present information.
So what if you had a program that contained ALL 3.5 edition hardback books. You could click on the rules you wanted and didn't want, and it would construct a rulebook just for your campaign. It would also analyze and grab needed info you didn't click on - say you clicked a PrC from the BoVD that required a specific feat from that book. That feat would be automatically added to the feat list for your "custom rulebook" without you having to dig for it and flag it yourself. Every rule you add will work like this - any other rules that are required for it to function will be automatically added to your list.
Now, pretty much all WoTC books (and most 3rd party d20 books) are organized the same way. The same chapters in the same order, things organized alphabetically inside them, etc. So it shouldn't be that difficult for a computer program to do this on the fly, and assemble a usable collection of the rules you want. Maybe you can save it as an HTML or .pdf file. If you have the time and paper, you can print out copies for your players, and they could use it as their "core rulebook" and need no other volumes.
I mentioned this to Schizm over the weekend, and he says that RPGToolkit is supposed to offer functionality like this, but as much as I admire the codemonkeys, RPGToolkit is, so far, nothing but long-lasting vaporware.
With proper tweaking, it might be possible to insert your own house rules, custom PrCs, spells, etc., into the system, and have them print out with everything else.
What do people think of this idea, the ability to make custom rulebooks that contain only the rules your campaign allows?