Have you ever tried the Drifter Challenge? I think it might be somewhat similar to what you're looking for. I love it, longest legacy type challenge I've ever played. I haven't played in that save since the gardening bug hit in the Eco Lifestyle pre-patch though. Here's a link to the rules:
The Drifter ChallengeMy own challenge,
One Month One World One Year involves living in a different world each real world month, but it's not a legacy type challenge. Sims start as a teen and stay a teen for 3 months, YA for 4 months, Adult for 4 months and are an elder for one month. You could adapt it however you like though. :) Perhaps try to do one generation per month, per world and follow the rest of the guidelines for goals? Just a thought...
Happy Simming! <3
