That seems a more economical way to get all the pieces you want to interact well. Using your army as the win condition is really a smart way to go when using Rhyas. I don't find myself assassinating with her very often. It's more likely to come from her army, tbh. I've found through some painful trial and error that the later I can activate her in a turn the better and you have that inbuilt. Keep in mind that you'll probably want to make room for a Suck in a few months or w/e they put it out.
EDIT: One situational synergy with the Seraph I can suggest makes Rhyas horrible STR a bonus. You can use Slipstream to place Rhyas 2" forward but within 1/2" of the Seraph (Flight makes this much easier), and make an auto hitting PUSH for another inch. Due to the discrepancy between their STR you actually can't fail on the push roll. I've used this little trick to get Rhyas the extra 1" you'd normally need to cast Dash for, leaving her with a full boat of fury for that last ditch assassination run. It's really more of 1/2" or 3/4" since you need to position Rhyas at an angle, but it's a simple way to get more threat. IT DOES REQUIRE PRACTICE, though, so watch out in competitive play!