Nope. The FAA did not care. MCAS was not made to keep the 737 MAX stable. It was designed so that it handled the same as any other 737. Without the MCAS, the FAA would have certified it but would have required crews to get difference training. Boeing was trying to avoid that since the NEO didn't need difference training.

No conspiracy theory here. It was not kept a secret. When operators ordered the plane, there was an option to attach MCAS to a second AOA. If MCAS was a secret, why would they have that as an option? The fact that they offered that as an option is odd and I hope we get to learn their reasoning. Also, I'm pretty sure that in the maintenance manuals they have several error codes associated with MCAS. If they were trying to hide MCAS, then that means they would have to hide it from the mechanics too.

There are lots of systems that pilots aren't told about or are overly simplified. That electrical schematic in your manual looks nothing like the actual electrical system. Pilots get the cliff-notes version. If I want to know where the static port for cabin pressure controller 1 is on my plane, my manuals won't help. Does that mean it is a secret? This looks more like an administrative/organization error. Whoever was in charge of updating the pilot manuals either didn't know about MCAS or didn't think it was important. Boeing did make a mistake by not including it, but there is little evidence (and evidence to the contrary) that Boeing was trying to keep it a secret.