Hey, I'm at Arribada working on the TimeLord project, which aims to solve this type of issue. There has been a delay getting started, but we have an initial prototype that supports 3.3 V to 5 V and allows control of two power and two signal outputs with timed events. However, we are looking to add the ability to trigger from an input as well to allow this kind of synchronization.

Unfortunately, we can't offer anything right now, but I would be very interested to hear what requirements you have, such as the input specs and the timing precision you require. This could help inform us what features we add to the next prototype. 

I've looked into adding external triggers to camera traps.  I've documented that effort here.  Basically, it involves board level work to hijack the trigger signal.  But as this signal is open drain, it's straightforward to wire-OR several of these signals from multiple cameras.  In your case, you can perform this OR operation using simple wireless units.

I'm afraid I don't see a way to abstract and extract the trigger functionality cleanly into a drop-in product.  Perhaps the best that can be done is to convert all participating cameras into slave units by replacing the IR sensor with a connector to which a master triggering source is attached.  This still requires individual board work, but is at least straightforward.