Inventing a class is like inventing a spell. It takes work-so what would a player character go through, to literally invent a prestige class? That's like inventing a martial art, its not easy to do and they probably couldn't do it without a very strong grasp on existing forms. A martial artist who invents a new style is probably a master or at least very capable fighter in several known forms. Likewise an inventor of a new arcane spellcasting prestige class is probably an archmage already versed in magic as its known. Not only that, but to be perfected, and "finished" it would probably have additions and changes made by the original master's students.

The last bit is key, because taking any non-homebrew PrC and claiming to be its inventor means that you would be the only person who could teach it to anyone; everyone who wanted to take the class would have to learn it from you or one of your disciples. At least for a time, you'd be claiming it only for yourself, making you "one of a kind".

Just for comparison, Grimm is a Shou Disciple, and he's the only Shou Disciple. This is actually because the PrC was deemed to powerful (namely flurrying with a 2-hander) but only after the only person who had taken was already 17th level. The decision at the time was to "Grandfather" the class -and it actually notes this at the bottom of the class page currently (albeit it should probably be at the top so no one gets excited before they read the whole thing). But even so-In Character he's not the only Shou Disciple, he's just the only "player character" who is one. If it seems a big deal to end up the only person with a class, think of how big a deal it would be to ask to be the only person allowed a class from the outset and not from circumstance.

It's heavy stuff.

But that's just the observation of a guy who likes lore, just laying out his thoughts on the forums.
^^;

Just flavor wise, I've no interest in altering mechanics.