The announcement mentioned another Intelligencier agent, the Unilluminated Mole, but to my knowledge they haven’t made an appearance yet. The roadmap also mentioned another Concern is to come, so we’ll be able to do what you said.
Personally, I don’t mind having various agents inactive - thematically, that may be taken as the necessary downtime for agent recuperation, upkeep of ships, lying down after a successful (or failed) infiltration etc. The only potential downside to having many more Agents would be having to scroll a lot when choosing the ones you wish to send out.
On the other hand, every additional Plot we’d be able to run concurrently would add to the “clickiness,” and I understand why there’s a sweet spot of how much “extra” revenue FBG might want to introduce through the Agent system.