So for example there would be a Ulthwe style origin that would unlock the improved guardians and jetbikes, a beit-tan one that lets you pick swooping hawks and scorpions*, and Wraith style option that would give wraithguard as troops and maybe allow a scoring wraithlord for every 2-3 squads. The wraithguard origin wouldn't have any additional restrictions on unit size so you could take a min. squad instead of having to take 10.
*This is the one area i'm not completely sold on, I picked hawks & scorpions because they have alternative deployments that don't require transports, they're fairly well rounded as far as aspects go, and I think allowing any aspect to be troops would be unbalanced. Honestly though if Dire Avengers become a bit more flexible aspect armies wouldn't need an origin, maybe something like sternguard ammo?
Beyond that the only suggestion I have is changing fire dragons, so they have heat lances, & tank hunter instead of melta guns. Its makes them a little less rounded, but they could be further from vehicles so they wouldn't get hurt by explosions and would be easier to hide.