Alternative universe can me kinda everything. E.g. what would your charries be and be like if they were born as someone else? (Marina for example would most likely be a madame if she wasn´t born as Targaryen and especially as future/ current queen xD) Othwise you can put them in a complete diffrent world, e.g. something more modern like the world of Avatar the last airbender/ legend of korra. (Lin for example would just be her badass spider chiefself though maybe with Daemon as her partner ^o^)
Now let your crazy minds wonder ♥
Also what surely is nice to think about are the relationships. E.g. will your char(ries) still will end up with the same or go for someone else?