I'm not even grunt yet, but I was wondering if there is a list for the classes if you prestige Demon-Hunter, Gladiator ect. Just to look at.. and then I believe you said we can submit a custom one but they are unlikely to happen???
There is
this which lists most prestiges, and yes, if you have an idea for a prestige it could be considered to be made offical but it must fit perfectly into the setting and not overlap with other prestiges already there. Do keep in mind though that at the moment we do not accept any applications or prestige proposals since we are still discussing how the new version for the prestiges will look and work.
I'm guessing custom classes, along with any sort of special variation, require that you know a -lot- lore wise to back it up, lay out exactly what you're getting as bonuses and losses (and I mean -exactly-, I've heard of people denied for being too vague or not giving enough on this), and simply the GMs have to trust you to be smart about your prestige class and have a character who would reasonably fit into that class.
Also, I'm sure it's possible to do almost anything as long as you have supporting lore and information on it (not necessarily lore stating that X happened before. For example there may never have been a mage who uses a bow to focus his magic, and effectively shoots 'fire arrows' of magic, despite them really being fire balls in essence. You can find supporting lore on how magic works (specifically elemental), lore on hunters and archers to just get an idea of what your character would be doing with that.)
I also think that there's a required amount of time you have to be here longer than grunt to try and apply? (I think 3 months?) Along with training and such relevant to such classes. (Demon hunters have to go through a long series of trials, it's pretty intense.)
The current process requires that players be Grunts and apply on a character than has been approved for at least a month. Depending on the prestige class for which a player is applying, a similar requirement may be in effect.