GW should've given each detachment two rules, like the Kroot detachment.
I know this topic has been talked to death, and that GW is never gonna treat this faction as a proper one, but GW should've given each detachment 2 rules, like how Kroot Hunting Pack has two seperate abilities to give your Krooy army two abilities to work with.
Not only that, but GW should've made them 2DP each, with the exception of Veiled Blade which should be 1DP, so that it can slot into any Imperial Agents army, regardless of the detachment you're running.
Off the top of my head, my ideas for the second rules would probably be lesser versions of their normal army rules, like some kind of movement ability for the Ordo Malleus detachment, a lesser or side-graded Oaths of Moment for the Deathwatch, some kind of dice manipulation for the Ordo Hereticus, and maybe some kind ability to generate Command Points while you control objectives for Imperialus Fleet.
If GW did this, you could essentially choose your army rule depending on how you wanted to play Imperial Agents, as well as your detachment rule.
The only detachment I would keep the same is Veiled Blade, not because I think it's strong, but because then the detachment could be made into a 1DP detachment that you could use to buff up your Assassins if you wanna take them.
I'd like to hear what you guys think of this idea though