I think it would be great if some of the WH1 races that are on the vortex map got a LL and became playable. I love playing Dwarfs, its my favorite faction, but the turn times on Mortal Empires map is excruciating once you get past turn 60-70, even with a top notch cpu. So i usually end up getting bored and feeling forced to play Vortex.
A easy way to get more out of the WH1 content would be to make them playable on the vortex map, like Greybeard's Prospectors, Top Knotz, Knights of the Flame, Bowmen of Oreon, Skeggi, Sudenburg etc. Just give them 1-2 legendary lords and some unique victory condition.
This could be sold as a dlc without having to own mortal empires dlc also.