Another thread on this subject:
https://forum.atlas-games.com/t/ars-magica-fantasy-setting/9057/15
something else similar
https://forum.atlas-games.com/t/what-kind-of-games-have-you-always-wanted-to-run-play/8884/1
https://forum.atlas-games.com/t/alternate-settings/8605/101
https://forum.atlas-games.com/t/the-history-of-the-order-is-a-lie-what-is-the/8416/1
My own alt setting ideas:
1.) I've always wanted to do an alt-setting where there is a loose Mageocracy that works with traditional nobles as "muscle". The PCs are trying to start a rebellion.
2.) On the subject of an early Order game, I'm running one in that started in 783 and is now at 801. Here are some related posts to that saga for anyone interested:
https://forum.atlas-games.com/t/historical-setting-breakthroughs-in-hermetic-magic/9385/10
https://forum.atlas-games.com/t/goals-of-the-titanoi/8852/1
https://forum.atlas-games.com/t/need-help-with-non-standard-companion-design/8701/1
https://forum.atlas-games.com/t/libraries-of-constantinople-circa-790ad/8531/1
https://forum.atlas-games.com/t/constantinople-circa-790/8521/1
https://forum.atlas-games.com/t/grand-tribunal-784/8364/1
https://forum.atlas-games.com/t/fortifications-in-the-700s/8157/1
https://forum.atlas-games.com/t/europe-in-the-late-700s/8145/1
https://forum.atlas-games.com/t/so-has-anyone-run-a-pre-schism-war-game/8127/1