I understand what you're saying however I'm not sure I agree. I'm assuming you're talking about Gideon and company rather than the new Aasimar. If you mean the new Aasimar then we already know Adam has said he needs to railroad them a bit. We know they need to get into the Rock Gnome dungeon to meet the other Snidge and co, it's really just a requirement for the game-play.
If you're referring to Gideon, Berg and Ramus then I do think they have motivations. They are prisoners sent on missions. They want to free themselves from their magical manacles which I think is their highest motivation right now. They've agreed to help out Snidge because he helped them.
Also we do know that Gideon has a deeper past however he has not had a chance to get into it yet. In the game I DM when we started I asked my players to give me five things they'd like to accomplish with their characters, I then used that to create some story arcs. However not everyone is comfortable with that, they may prefer to simply interact with the world that Adam has created here.
I think if Gideon is resurrected we will have some touch-points on his past after they free themselves. However my preference is for him to continue with Raziel, Warlock's can be really fun to DM for because a Warlock's Patron will usually constantly fuck with you, causing all kinds of havoc and putting you in weird situations.
Just my 2 cents.