Instead of just having 1 quest at a time on your credo, it automatically adds one on a timer.
If you have NO current quests on your credo it adds one instantly just like now
If you already have X current quests on your credo if adds one in (X^2) days (so after 1 day you'll have two quests concurrently.. after 4 days you'll have 3 quests.. etc.)
Finishing a quest does NOT instantly replace it. So if you have 3 quests and finish one of them, it'll give you +1 to credo progress and you'll still just have the remaining 2 quests. And after 4 days it'll add a third.
Abandoning ANY of the quests on your list gives -1 to progress just like now. And does not replace it.
The time it takes to add a quest is subject to debate, I'm not sure about it. But the basic idea is that the more quests you have, the harder it'll be to add another one.
I figure this would soften the blow just a little bit of getting a quest that's a real bitch titty ("tame a horse"). You can work towards taming a horse, and in the meantime you'll get another, hopefully more doable quest in 1 day.