Nope.
I've installed all of my F/A systems in exactly the manner described in the original post.
The NEC is oriented towards fire hazards.
The weight of the trivial materials tucked inside such junction boxes is a joke.
If ANYTHING goes awry -- the F/A system goes into ALERT mode -- which is not the same as an alarm.
In ALERT mode the system informs the dispatcher to promptly send out a tech to service the system. The modern, digital, systems will even point out the faulting address.
If, at any time, a bona fide fire / emergency occur, the system will fire off into full ALARM mode -- over-riding the ALERT mode.
EVERY F/A system uses this priority sequence. No system is allowed to fault out -- and fail to notify the dispatcher and those inside the structure.
&&&
You're actually over engineering your scheme... a fault common to electricians the world over.
