So I had an idea for a campaign that starts at the dawn of civilization. Races haven't developed from a generic humanoid yet and are at a stone age level of technology.
The players and some NPCs from other clans get reincarnated every generation or every few generations to help guide their people. As they guide their clan over generations it would begin to develop racial traits and the characters would carry some of their knowledge from past lives with them. Players would probably have to discover things like divine and arcane magic, ki or other more special abilities.
Starting off it would look something like this
15 point buy
Racial modifiers +2 to one stat
level 1 characters
no spell-casting at this point
After a few sessions of playing those characters through a few key events, say their clan being attacked by a fierce predator that they must track down and slay and later they make first contact with another clan; they reincarnate Making new characters that would retain something from their previous life, probably a skill point.
Each character would only be played for a couple sessions, but over time their clan would gain racial traits and their characters would retain more and more information from past lives eventually being able to retain feats or low level class features from previous lives. over time the level of the characters would go up as well.
Thoughts?
We have done something similar. Though we started at the first agricultural settlement for the 1st era (no wizards or other "Trained" classes) and jumped hundreds of years with the 2nd character (could be a wizard, but there were strict rules on what spells you could learn). There are plans for a future campaign, but we haven't done it yet.
My suggestions;
- I think if you are going to start so early then keep the character arcs short. 1 or 2 levels.
- Have the jumps be longer than a couple of generations. They only come back when there is a great need and their families/peoples are facing a great peril.
- Allow the players to keep the experience from character to character. DON'T start every new character at 1st level.
- Have items that get handed down through the family lines and change and grow through time.
Games where time passes and the world changes and develops can be the most rewarding experiences of any roleplaying game.
But it can also be really challenging - it is a lot of work to create a world with verisimilitude, especially if it's changing and growing through time. The challenges, choices, and consequences the PCs face have to feel real, and this can be hard when the PCs are supposed to be all but literally 'creating the world' - if a PC expects to be able to say "I found an order of elvish mage knights - they battle evil through the generations but also collect intelligence, do spell research, and make magic items all so they can give them to me when I come back" may not be happy when they reincarnate and are told that there's been a schism in the order, and three separate groups of knights are warring, each claiming to be the real and loyal sect, and the they haven't had any time to make her magic items at all.
I strongly recommend that you include various/diverse reoccuring characters across the ages - whether these are (demi)gods, immortals, time travelers/'stasis pod people', necromancers, or fellow reincarnateors. One of the best parts of an ongoing campaign like this is that the characters have time to grow and change, and to develop connections in the world - if the PCs only meet a batch of NPCs for a couple of sessions/levels before they reincarnate and everyone they ever knew is going to die again anyway, not only will they miss out on those cool interrelationships, they're more likely to treat the world/NPCs/etc as semi-disposable.
I'd consider using a mini-game/side game to handle the time passing, world changing, races/subraces appearing, etc - for example Dawn of Worlds is, in my opinion a really cool little game collaborative world building game - the game concept you describe would start more like the 'second age' of DoW, but you could pregen a first age - or let them do it with you!