Yes, that is what I do now. Once the player's got a bare-bones PC ready [quick backstory, confirmed sheet and solid concept], I start them out on their prologue. I do this for three reasons:In regard to all of the above, has anybody ever started a game one or two characters at a time as people get their characters ready? Just throw them into the game and then the next and the next, lather, rinse, repeat, as each player gets their character together?...
1/ To give the player some RP while they finish off some of the details before joining the rest of the group. [It's hard to introduce a new PC when the others are halfway through a mission. It's either a prologue or they wait. I offer the option to wait if they'd like to - none has said yes to this yet].
2/ To infodump background info.
3/ To allow both player and myself to understand what kind of PC they're playing. Also allows players to learn the pbp / game format.
My current pbp game literally started with one ready-to-play PC.